Avoid some unexpected recursions because of yields to event loop...

... See code comments.

Not proved to be a cause of data loss bugs, but they caused surprises when
trying to step in the debugger.

src/ProjectAudioManager.cpp

@@ -910,16 +910,21 @@ void ProjectAudioManager::OnAudioIOStopRecording()
 
             history.ModifyState( true ); // this might fail and throw
 
-            ShowWarningDialog(&window, wxT("DropoutDetected"), XO("\
+            // CallAfter so that we avoid any problems of yielding
+            // to the event loop while still inside the timer callback,
+            // entering StopStream() recursively
+            wxTheApp->CallAfter( [&] {
+               ShowWarningDialog(&window, wxT("DropoutDetected"), XO("\
 Recorded audio was lost at the labeled locations. Possible causes:\n\
 \n\
 Other applications are competing with Audacity for processor time\n\
 \n\
 You are saving directly to a slow external storage device\n\
 "
-               ),
-               false,
-               XXO("Turn off dropout detection"));
+                  ),
+                  false,
+                  XXO("Turn off dropout detection"));
+            });
          }
       }
    }