Core/Misc: Fix vsnprintf usage in ASSERT()

Fix vsnprintf to follow standard definition and not some old VC++ behavior, not requiring to include the '\0' character in the count parameter

(cherry picked from commit eee1f2cadf)

src/common/Debugging/Errors.cpp

@@ -59,7 +59,7 @@ namespace
         va_end(len);
 
         formatted.resize(length);
-        vsnprintf(&formatted[0], length, format, args);
+        vsnprintf(&formatted[0], length + 1, format, args);
 
         return formatted;
     }