HTTP: fix stack-buffer-overflow (#1768)

```
==24879==ERROR: AddressSanitizer: stack-buffer-overflow on address 0x7fa085b31e60 at pc 0x55cc63f203e2 bp 0x7ffc9ec91b10 sp 0x7ffc9ec91298
READ of size 17 at 0x7fa085b31e60 thread T0
    #0 0x55cc63f203e1 in printf_common(void*, char const*, __va_list_tag*) asan_interceptors.cpp.o
    #1 0x55cc63f20769 in vsnprintf (/home/ivan/svnrepos/nDPI/fuzz/fuzz_process_packet_with_main+0x50e769) (BuildId: cce2b6b1344bfd0bdc9626fef604c2b3caad485b)
    #2 0x55cc63f22210 in __interceptor_snprintf (/home/ivan/svnrepos/nDPI/fuzz/fuzz_process_packet_with_main+0x510210) (BuildId: cce2b6b1344bfd0bdc9626fef604c2b3caad485b)
    #3 0x55cc6420fc76 in ndpi_check_http_server /home/ivan/svnrepos/nDPI/src/lib/protocols/http.c:668:4
    #4 0x55cc6420344b in check_content_type_and_change_protocol /home/ivan/svnrepos/nDPI/src/lib/protocols/http.c:742:5
    #5 0x55cc642031ce in check_content_type_and_change_protocol /home/ivan/svnrepos/nDPI/src/lib/protocols/http.c:737:7
    #6 0x55cc641fac9f in ndpi_check_http_tcp /home/ivan/svnrepos/nDPI/src/lib/protocols/http.c:1352:4
    #7 0x55cc641f2fd5 in ndpi_search_http_tcp /home/ivan/svnrepos/nDPI/src/lib/protocols/http.c:1461:3
    #8 0x55cc64085275 in check_ndpi_detection_func /home/ivan/svnrepos/nDPI/src/lib/ndpi_main.c:5580:6
    #9 0x55cc64085c87 in check_ndpi_tcp_flow_func /home/ivan/svnrepos/nDPI/src/lib/ndpi_main.c:5628:12
    #10 0x55cc64085927 in ndpi_check_flow_func /home/ivan/svnrepos/nDPI/src/lib/ndpi_main.c:5647:12
    #11 0x55cc64095fcb in ndpi_detection_process_packet /home/ivan/svnrepos/nDPI/src/lib/ndpi_main.c:6458:15
    #12 0x55cc63fd08b4 in LLVMFuzzerTestOneInput /home/ivan/svnrepos/nDPI/fuzz/fuzz_process_packet.c:29:5
    #13 0x55cc63fd09f7 in main /home/ivan/svnrepos/nDPI/fuzz/fuzz_process_packet.c:101:17
    #14 0x7fa0880fb082 in __libc_start_main /build/glibc-SzIz7B/glibc-2.31/csu/../csu/libc-start.c:308:16
    #15 0x55cc63efb45d in _start (/home/ivan/svnrepos/nDPI/fuzz/fuzz_process_packet_with_main+0x4e945d) (BuildId: cce2b6b1344bfd0bdc9626fef604c2b3caad485b)

Address 0x7fa085b31e60 is located in stack of thread T0 at offset 96 in frame
    #0 0x55cc6420f1bf in ndpi_check_http_server /home/ivan/svnrepos/nDPI/src/lib/protocols/http.c:644

  This frame has 5 object(s):
    [32, 36) 'a' (line 653)
    [48, 52) 'b' (line 653)
    [64, 68) 'c' (line 653)
    [80, 96) 'buf' (line 654)
    [112, 176) 'msg' (line 662) <== Memory access at offset 96 partially underflows this variable

```
Found by oss-fuzzer
See: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=52229

src/lib/protocols/http.c

@@ -655,7 +655,7 @@ static void ndpi_check_http_server(struct ndpi_detection_module_struct *ndpi_str
       u_int i, j, a, b, c;
       char buf[16] = { '\0' };
 
-      for(i=off, j=0; (i<server_len) && (j<sizeof(buf))
+      for(i=off, j=0; (i<server_len) && (j<sizeof(buf)-1)
 	    && (isdigit(server[i]) || (server[i] == '.')); i++)
 	buf[j++] = server[i];