Prevent to turn screen off if no control

If --no-control is set, then the controller is not initialized (both in
the client and the server), so it is not possible to control the device
to turn its screen off.

See <#608>.

app/src/main.c

@@ -414,6 +414,11 @@ parse_args(struct args *args, int argc, char *argv[]) {
         }
     }
 
+    if (args->no_control && args->turn_screen_off) {
+        LOGE("Cannot request to turn screen off if control is disabled");
+        return false;
+    }
+
     return true;
 }