Explicitly initialize two local variables to 0 (sonic-net#3046)

GCC 12 (in Debian Bookworm) claims that on armhf targets, the `lower`
local variable in `Orch::generateIdListFromMap` could potentially be
used uninitialized a few lines later when it's being converted to a
string. I don't see how that could be the case here, since if the string
is being printed, the only code path where this is possible requires
`lower` to have been set to something.

To silence the warning, set both `lower` and `upper` to 0 explicitly.

orchagent/orch.cpp

@@ -697,7 +697,7 @@ set<string> Orch::generateIdListFromMap(unsigned long idsMap, sai_uint32_t maxId
 {
     unsigned long currentIdMask = 1;
     bool started = false, needGenerateMap = false;
-    sai_uint32_t lower, upper;
+    sai_uint32_t lower = 0, upper = 0;
     set<string> idStringList;
     for (sai_uint32_t id = 0; id <= maxId; id ++)
     {