Report server connection state

We must distinguish 3 cases for await_for_server():
 - an error occurred
 - no error occurred, the device is connected
 - no error occurred, the device is not connected (user requested to
   quit)

For this purpose, use an additional output parameter to indicate if the
device is connected (only set when no error occurs).

Refs #3085 <https://github.com/Genymobile/scrcpy/pull/3085>

app/src/scrcpy.c

@@ -168,19 +168,22 @@ event_loop(struct scrcpy *s) {
     return false;
 }
 
+// Return true on success, false on error
 static bool
-await_for_server(void) {
+await_for_server(bool *connected) {
     SDL_Event event;
     while (SDL_WaitEvent(&event)) {
         switch (event.type) {
             case SDL_QUIT:
                 LOGD("User requested to quit");
-                return false;
+                *connected = false;
+                return true;
             case EVENT_SERVER_CONNECTION_FAILED:
                 LOGE("Server connection failed");
                 return false;
             case EVENT_SERVER_CONNECTED:
                 LOGD("Server connected");
+                *connected = true;
                 return true;
             default:
                 break;
@@ -351,7 +354,14 @@ scrcpy(struct scrcpy_options *options) {
     sdl_configure(options->display, options->disable_screensaver);
 
     // Await for server without blocking Ctrl+C handling
-    if (!await_for_server()) {
+    bool connected;
+    if (!await_for_server(&connected)) {
+        goto end;
+    }
+
+    if (!connected) {
+        // This is not an error, user requested to quit
+        ret = true;
         goto end;
     }