libobs: fix the pending stop trick

Regression introduced by dc4e20500: while the stop detection is pending,
it should still return false so the rest of the discard code can run.
Otherwise, the source audio will remain in the buffer, lagging the
source and triggering audio buffering increases until max audio
buffering is reached.

libobs/obs-audio.c

@@ -116,7 +116,7 @@ static bool discard_if_stopped(obs_source_t *source, size_t channels)
 			blog(LOG_DEBUG, "doing pending stop trick: '%s'",
 			     source->context.name);
 #endif
-			return true;
+			return false;
 		}
 
 		for (size_t ch = 0; ch < channels; ch++)