drop() no longer calls midiOutReset

Fixes Boddlnagg#122

On Windows, midiOutReset was being called before midiOutClose,
presumably to cancel any pending output. This caused extra MIDI
commands to be sent. Instead, we now call midiOutClose repeatedly
until it's no longer blocked by pending output.

src/backend/winmm/mod.rs

@@ -21,7 +21,7 @@ use windows::Win32::Media::Audio::{
     midiInOpen, midiInPrepareHeader, midiInReset, midiInStart,
     midiInStop, midiInUnprepareHeader, midiOutClose,
     midiOutGetDevCapsW, midiOutGetNumDevs, midiOutLongMsg, midiOutOpen,
-    midiOutPrepareHeader, midiOutReset, midiOutShortMsg,
+    midiOutPrepareHeader, midiOutShortMsg,
     midiOutUnprepareHeader, midiInMessage, midiOutMessage,
     HMIDIIN, HMIDIOUT, MIDIHDR, MIDIINCAPSW, MIDIOUTCAPSW, CALLBACK_FUNCTION, CALLBACK_NULL,
     MIDIERR_NOTREADY, MIDIERR_STILLPLAYING,
@@ -533,9 +533,12 @@ impl MidiOutputConnection {
 
 impl Drop for MidiOutputConnection {
     fn drop(&mut self) {
-        unsafe {
-            midiOutReset(self.out_handle);
-            midiOutClose(self.out_handle);
+        loop {
+            let result = unsafe { midiOutClose(self.out_handle) };
+            if result == MIDIERR_STILLPLAYING {
+                sleep(Duration::from_millis(1));
+                continue;
+            } else { break; }
         }
     }
 }