Prevent tdm crash if window manager or compositor do not start

(cherry picked from commit 8a80c7f3df)

kdm/kfrontend/kgapp.cpp

@@ -452,6 +452,7 @@ kg_main( const char *argv0 )
 	KGVerify::done();
 
 	if (comp) {
+		if (comp->isRunning()) {
 			if (_compositor == "kompmgr") {
 				// Change process UID
 				// Get user UID
@@ -468,9 +469,11 @@ kg_main( const char *argv0 )
 			}
 			comp->closeStdin();
 			comp->detach();
+		}
 		delete comp;
 	}
 	if (kwin) {
+		if (kwin->isRunning()) {
 			if (login_session_wm.endsWith("/startkde") || (login_session_wm == "failsafe")) {
 				kwin->closeStdin();
 				kwin->detach();
@@ -480,6 +483,7 @@ kg_main( const char *argv0 )
 				kwin->kill();
 				dcop->kill();
 			}
+		}
 		delete kwin;
 		delete dcop;
 	}