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, 8 insertions, 1 deletions

diff --git a/engines/m4/midi.cpp b/engines/m4/midi.cpp
index f130ddc3b5..3a6475da89 100644
--- a/engines/m4/midi.cpp
+++ b/engines/m4/midi.cpp
@@ -83,10 +83,16 @@ int MidiPlayer::open() {
 	return 0;
 }
 
+bool MidiPlayer::isOpen() const {
+	return _driver && _driver->isOpen();
+}
+
 void MidiPlayer::close() {
 	stopMusic();
-	if (_driver)
+	if (_driver) {
 		_driver->close();
+		delete _driver;
+	}
 	_driver = 0;
 }
 
diff --git a/engines/m4/midi.h b/engines/m4/midi.h
index 8344f8d485..a631cec2cb 100644
--- a/engines/m4/midi.h
+++ b/engines/m4/midi.h
@@ -54,6 +54,7 @@ public:
 
 	//MidiDriver interface implementation
 	int open();
+	bool isOpen() const;
 	void close();
 	void send(uint32 b);