"Small Deploy with Network Filesystem" crashes Editor when exported end exits

[Firepal]

Godot version:

3.2.4.rc (built earlier today)

OS/device including version:

Editor: Windows 10
Target: Oculus Quest 2 (most likely affects any Android device)

Issue description:

Exiting an Android-exported game with "Small Deploy with Network Filesystem" enabled, causes the Editor to crash and print:

WARNING: Thread::~Thread: A Thread object has been destroyed without wait_to_finish() having been called on it. Please do so to ensure correct cleanup of the thread.
     At: core\os\thread.cpp:117
ERROR: EditorFileServer::_subthread_start: Condition "err != OK" is true.
   At: editor\fileserver\editor_file_server.cpp:115

This also breaks using One-Click Deploy more than once, as it intentionally closes the game on the exported end.

Steps to reproduce:

• With a very recently-built 3.2.x Godot, create a project with an Android export preset
• Enable "Small Deploy with Network Filesystem"
• One-Click Deploy twice

[akien-mga]

Tested with 3.2.4 RC 3 on Linux, exporting to a Xiaomi Pocophone F1, and I can reproduce the issue. It's likely caused by Thread changes in #45618.

I could also reproduce it with a build from latest 3.2 (36bec66):

WARNING: ~Thread: A Thread object has been destroyed without wait_to_finish() having been called on it. Please do so to ensure correct cleanup of the thread.
   At: core/os/thread.cpp:117.
ERROR: _subthread_start: Condition "err != OK" is true.
   At: editor/fileserver/editor_file_server.cpp:115.
[Thread 0x7fff82ffe640 (LWP 450049) exited]
terminate called after throwing an instance of 'std::system_error'
  what():  Invalid argument

Thread 26 "godot-3.2" received signal SIGABRT, Aborted.
[Switching to Thread 0x7fff8da8a640 (LWP 449251)]
0x00007ffff7aa04b0 in raise () from /lib64/libc.so.6
(gdb) bt
#0  0x00007ffff7aa04b0 in raise () from /lib64/libc.so.6
#1  0x00007ffff7a8b526 in abort () from /lib64/libc.so.6
#2  0x0000000001702e2b in __gnu_cxx::__verbose_terminate_handler () at ../../../../libstdc++-v3/libsupc++/vterminate.cc:95
#3  0x00000000046eb316 in __cxxabiv1::__terminate (handler=<optimized out>) at ../../../../libstdc++-v3/libsupc++/eh_terminate.cc:48
#4  0x00000000046eb381 in std::terminate () at ../../../../libstdc++-v3/libsupc++/eh_terminate.cc:58
#5  0x00000000046eb4d4 in __cxxabiv1::__cxa_throw (obj=obj@entry=0x7fff78000c60, tinfo=tinfo@entry=0x60ca4e8 <typeinfo for std::system_error>, dest=dest@entry=0x47644a0 <std::system_error::~system_error()>)
    at ../../../../libstdc++-v3/libsupc++/eh_throw.cc:95
#6  0x0000000001704c2f in std::__throw_system_error (__i=22) at ../../../../../libstdc++-v3/src/c++11/system_error.cc:338
#7  0x000000000476498c in std::thread::join (this=0x7fff78000b98) at ../../../../../libstdc++-v3/src/c++11/thread.cc:113
#8  0x00000000043ca454 in Thread::wait_to_finish (this=0x7fff78000b90) at core/os/thread.cpp:96
#9  0x0000000002d5ffc6 in EditorFileServer::_thread_start (s=0x6ab3180) at editor/fileserver/editor_file_server.cpp:303
#10 0x00000000043ca28a in Thread::callback (p_self=0x6ab32c0, p_settings=..., p_callback=0x2d5fd34 <EditorFileServer::_thread_start(void*)>, p_userdata=0x6ab3180) at core/os/thread.cpp:68
#11 0x00000000043cb00b in std::__invoke_impl<void, void (*)(Thread*, Thread::Settings const&, void (*)(void*), void*), Thread*, Thread::Settings, void (*)(void*), void*> (
    __f=@0xa44f388: 0x43ca21e <Thread::callback(Thread*, Thread::Settings const&, void (*)(void*), void*)>) at /usr/include/c++/10/bits/invoke.h:60
#12 0x00000000043cae8e in std::__invoke<void (*)(Thread*, Thread::Settings const&, void (*)(void*), void*), Thread*, Thread::Settings, void (*)(void*), void*> (
    __fn=@0xa44f388: 0x43ca21e <Thread::callback(Thread*, Thread::Settings const&, void (*)(void*), void*)>) at /usr/include/c++/10/bits/invoke.h:95
#13 0x00000000043cad49 in std::thread::_Invoker<std::tuple<void (*)(Thread*, Thread::Settings const&, void (*)(void*), void*), Thread*, Thread::Settings, void (*)(void*), void*> >::_M_invoke<0ul, 1ul, 2ul, 3ul, 4ul> (this=0xa44f368) at /usr/include/c++/10/thread:264
#14 0x00000000043cacae in std::thread::_Invoker<std::tuple<void (*)(Thread*, Thread::Settings const&, void (*)(void*), void*), Thread*, Thread::Settings, void (*)(void*), void*> >::operator() (this=0xa44f368)
    at /usr/include/c++/10/thread:271
#15 0x00000000043cac92 in std::thread::_State_impl<std::thread::_Invoker<std::tuple<void (*)(Thread*, Thread::Settings const&, void (*)(void*), void*), Thread*, Thread::Settings, void (*)(void*), void*> > >::_M_run (this=0xa44f360) at /usr/include/c++/10/thread:215
#16 0x0000000004764740 in std::execute_native_thread_routine (__p=0xa44f360) at ../../../../../libstdc++-v3/src/c++11/thread.cc:80
#17 0x00007ffff7d6fdea in start_thread () from /lib64/libpthread.so.0
#18 0x00007ffff7b5afff in clone () from /lib64/libc.so.6