Skip stale PID dialog on macOS

The Sys_Dialog call that prompts about safe video settings after an
abnormal exit uses NSAlert on macOS, which can block indefinitely when
called before the window server connection is fully established. This
leaves the process hung with no visible UI. Skip the dialog on macOS
while preserving it on other platforms.

Author: jackharrhy

code/qcommon/common.c

@@ -2773,7 +2773,7 @@ void Com_Init( char *commandLine ) {
 	Sys_Init();
 
 	if( Sys_WritePIDFile( ) ) {
-#ifndef DEDICATED
+#if !defined(DEDICATED) && !defined(MACOS_X)
 		const char *message = "The last time " CLIENT_WINDOW_TITLE " ran, "
 			"it didn't exit properly. This may be due to inappropriate video "
 			"settings. Would you like to start with \"safe\" video settings?";