MidiService: clear status when device unbound

This can help prevent MIDI input ports from getting
stuck in the open position.

Bug: 210724686
Test: see bug for repro steps
Test: atest CtsMidiTestCases
Test: https://source.android.com/devices/audio/midi_test.html
Test: Check status with:  adb shell dumpsys midi
Change-Id: I9fe45eeb2d51356d114ae5a1a175e3d1f6977328

services/midi/java/com/android/server/midi/MidiService.java

@@ -340,6 +340,11 @@ public class MidiService extends IMidiManager.Stub {
 
                 IBinder binder = server.asBinder();
                 mDevicesByServer.remove(binder);
+                // Clearing mDeviceStatus is needed because setDeviceStatus()
+                // relies on finding the device in mDevicesByServer.
+                // So the status can no longer be updated after we remove it.
+                // Then we can end up with input ports that are stuck open.
+                mDeviceStatus = null;
 
                 try {
                     server.closeDevice();