Check for null pointer

This fixes a crash when the SESSION_MANAGER enviroment variable
is not set.

Signed-off-by: Mavridis Philippe <mavridisf@gmail.com>

src/qt_qt_wrapper.cpp

@@ -413,7 +413,9 @@ void createTQApp()
 		initKdeSettings();
 
 #ifndef USE_SOLARIS
-		setenv("SESSION_MANAGER", sessionEnv, 1);
+		if (sessionEnv) {
+			setenv("SESSION_MANAGER", sessionEnv, 1);
+		}
 #else
 		char *tempEnv=(char *)malloc(strlen(sessionEnv)+strlen("SESSION_MANAGER")+2);
 		sprintf(tempEnv, "SESSION_MANAGER=%s", sessionEnv);