(trunk qt) #3938 "The default config directory isn't created by the Qt client" -- fixed.

Summary says it all. Patch by luksan with minor formatting changes (and, no doubt, a new bug) by me.

qt/app.cc

@@ -136,9 +136,15 @@ MyApp :: MyApp( int& argc, char ** argv ):
     }
 
     // set the fallback config dir
-    if( configDir == 0 )
+    if( configDir == 0 ) {
         configDir = tr_getDefaultConfigDir( MY_CONFIG_NAME );
 
+        // ensure the config directory exists
+        QDir dir( configDir );
+        if( !dir.exists() )
+            dir.mkpath( configDir );
+    }
+
     // is this the first time we've run transmission?
     const bool firstTime = !QFile(QDir(configDir).absoluteFilePath("settings.json")).exists();