AUDIO: Add pure virtual MidiDriver::isOpen() method

This in turn enables modifying MidiDriver_MPU401::close() to allow
it to be called on a midi driver that has not yet been opened.

The specific issue that triggered me to make these changes was a
crash-upon-quit in HUGO, caused by it instantiating a midi driver,
then encountering an error (missing hugo.dat) *before* having
opened the new midi driver; the general cleanup code then tries
to close the (not yet opened) midi driver -> kaboom

Also fixed some engines which were leaking MidiDriver instances.

2 files changed, 4 insertions, 1 deletions

diff --git a/engines/queen/music.cpp b/engines/queen/music.cpp
index 4dc698dac9..044717878b 100644
--- a/engines/queen/music.cpp
+++ b/engines/queen/music.cpp
@@ -78,8 +78,10 @@ MidiMusic::MidiMusic(QueenEngine *vm)
 			_driver->property(MidiDriver::PROP_CHANNEL_MASK, 0x03FE);
 		}
 	}
+	assert(_driver);
 
-	_driver->open();
+	int ret = _driver->open();
+	assert(ret == 0);
 	_driver->setTimerCallback(this, &timerCallback);
 
 	if (_nativeMT32)
diff --git a/engines/queen/music.h b/engines/queen/music.h
index fe45d56fde..50f7b3d255 100644
--- a/engines/queen/music.h
+++ b/engines/queen/music.h
@@ -58,6 +58,7 @@ public:
 
 	//MidiDriver interface implementation
 	int open() { return 0; }
+	bool isOpen() const { return true; }
 	void close() {}
 	void send(uint32 b);