Fix recursive faults in Window crash logger due to message box event loop.

src/os/windows/win32.cpp

@@ -34,6 +34,8 @@
 #undef strncat
 #undef strncpy
 
+bool _in_event_loop_post_crash;
+
 static bool _has_console;
 static bool _cursor_disable = true;
 static bool _cursor_visible = true;
@@ -82,6 +84,7 @@ bool LoadLibraryList(Function proc[], const char *dll)
 
 void ShowOSErrorBox(const char *buf, bool system)
 {
+	_in_event_loop_post_crash = true;
 	MyShowCursor(true);
 	MessageBox(GetActiveWindow(), OTTD2FS(buf), _T("Error!"), MB_ICONSTOP);
 }