Changed PULSEAUDIO_FlushRecording() to only flush audio present when called.

When the flushing is not able to keep up with the audio stream coming in,
it will end up flushing forever and block API clients from getting any audio.

Fixes #9706

(cherry picked from commit 24693ac2857e614a3f3c84f8bbdca17b3423dd4c)

src/audio/pulseaudio/SDL_pulseaudio.c

@@ -497,7 +497,7 @@ static void PULSEAUDIO_FlushCapture(_THIS)
 {
     struct SDL_PrivateAudioData *h = this->hidden;
     const void *data = NULL;
-    size_t nbytes = 0;
+    size_t nbytes = 0, buflen = 0;
 
     PULSEAUDIO_pa_threaded_mainloop_lock(pulseaudio_threaded_mainloop);
 
@@ -507,19 +507,19 @@ static void PULSEAUDIO_FlushCapture(_THIS)
         h->capturelen = 0;
     }
 
-    while (SDL_AtomicGet(&this->enabled) && (PULSEAUDIO_pa_stream_readable_size(h->stream) > 0)) {
+    buflen = PULSEAUDIO_pa_stream_readable_size(h->stream);
+    while (SDL_AtomicGet(&this->enabled) && (buflen > 0)) {
         PULSEAUDIO_pa_threaded_mainloop_wait(pulseaudio_threaded_mainloop);
         if ((PULSEAUDIO_pa_context_get_state(pulseaudio_context) != PA_CONTEXT_READY) || (PULSEAUDIO_pa_stream_get_state(h->stream) != PA_STREAM_READY)) {
             /*printf("PULSEAUDIO DEVICE FAILURE IN FLUSHCAPTURE!\n");*/
             SDL_OpenedAudioDeviceDisconnected(this);
             break;
         }
-
-        if (PULSEAUDIO_pa_stream_readable_size(h->stream) > 0) {
-            /* a new fragment is available! Just dump it. */
-            PULSEAUDIO_pa_stream_peek(h->stream, &data, &nbytes);
-            PULSEAUDIO_pa_stream_drop(h->stream); /* drop this fragment. */
-        }
+        /* a fragment of audio present before FlushCapture was call is
+           available! Just drop it. */
+        PULSEAUDIO_pa_stream_peek(h->stream, &data, &nbytes);
+        PULSEAUDIO_pa_stream_drop(h->stream);
+        buflen -= nbytes;
     }
 
     PULSEAUDIO_pa_threaded_mainloop_unlock(pulseaudio_threaded_mainloop);