Windows: Make alert message box use MB_TASKMODAL

This flag pauses the current running thread, allowing for the user to see the
alert and acknowledge it before the thread continues (and e.g. crashes :)).

Thanks to @SuperUserNameMan for finding it.
Ref: https://msdn.microsoft.com/en-us/library/windows/desktop/ms645505(v=vs.85).aspx

platform/windows/os_windows.cpp

@@ -1343,7 +1343,7 @@ void OS_Windows::vprint(const char* p_format, va_list p_list, bool p_stderr) {
 void OS_Windows::alert(const String& p_alert,const String& p_title) {
 
 	if (!is_no_window_mode_enabled())
-		MessageBoxW(NULL,p_alert.c_str(),p_title.c_str(),MB_OK|MB_ICONEXCLAMATION);
+		MessageBoxW(NULL, p_alert.c_str(), p_title.c_str(), MB_OK | MB_ICONEXCLAMATION | MB_TASKMODAL);
 	else
 		print_line("ALERT: "+p_alert);
 }