Fix detection of invalid music drivers specified via command line.

Along with it documented that "0" is a special device handle
for the invalid device. Now getDeviceHandle returns 0, when
the identified device could not be found.

Also getMusicType now returns MT_INVALID (newly introduced),
when a non existing device was specified.

svn-id: r50470

3 files changed, 15 insertions, 6 deletions

diff --git a/base/main.cpp b/base/main.cpp
index a668c453d4..d40c912bf8 100644
--- a/base/main.cpp
+++ b/base/main.cpp
@@ -346,9 +346,9 @@ extern "C" int scummvm_main(int argc, const char * const argv[]) {
 	// We can't check this before loading the music plugins.
 	// On the other hand we cannot load the plugins before we know the file paths (in case of external plugins).
 	if (settings.contains("music-driver")) {
-		if (MidiDriver::getMusicType(MidiDriver::getDeviceHandle(settings["music-driver"])) == MT_NULL) {
-				warning("Unrecognized music driver '%s'\nSwitching to default device.", settings["music-driver"].c_str());
-				settings["music-driver"] = "auto";
+		if (MidiDriver::getMusicType(MidiDriver::getDeviceHandle(settings["music-driver"])) == MT_INVALID) {
+			warning("Unrecognized music driver '%s'. Switching to default device.", settings["music-driver"].c_str());
+			settings["music-driver"] = "auto";
 		}
 	}
 
diff --git a/sound/mididrv.cpp b/sound/mididrv.cpp
index 80c8ae9c22..26d43ebfe1 100644
--- a/sound/mididrv.cpp
+++ b/sound/mididrv.cpp
@@ -95,7 +95,7 @@ MusicType MidiDriver::getMusicType(MidiDriver::DeviceHandle handle) {
 		}
 	}
 	
-	return MT_AUTO;
+	return MT_INVALID;
 }
 
 Common::String MidiDriver::getDeviceString(DeviceHandle handle, DeviceStringType type) {
@@ -256,10 +256,11 @@ MidiDriver::DeviceHandle MidiDriver::getDeviceHandle(const Common::String &ident
 	for (MusicPlugin::List::const_iterator m = p.begin(); m != p.end(); m++) {
 		MusicDevices i = (**m)->getDevices();
 		for (MusicDevices::iterator d = i.begin(); d != i.end(); d++) {
-			if (identifier.equals(d->getCompleteId()) || identifier.equals(d->getCompleteName()))
+			if (identifier.equals(d->getCompleteId()) || identifier.equals(d->getCompleteName())) {
 				return d->getHandle();
+			}
 		}
 	}
 
-	return getDeviceHandle("auto");
+	return 0;
 }
diff --git a/sound/mididrv.h b/sound/mididrv.h
index ff6ce01295..5fffd430fb 100644
--- a/sound/mididrv.h
+++ b/sound/mididrv.h
@@ -50,6 +50,7 @@ namespace Common { class String; }
  * Music types that music drivers can implement and engines can rely on.
  */
 enum MusicType {
+	MT_INVALID = -1,    // Invalid output
 	MT_AUTO = 0,        // Auto
 	MT_NULL,            // Null
 	MT_PCSPK,           // PC Speaker
@@ -101,6 +102,13 @@ enum MidiDriverFlags {
  */
 class MidiDriver {
 public:
+	/**
+	 * The device handle.
+	 *
+	 * The value 0 is reserved for an invalid device for now.
+	 * TODO: Maybe we should use -1 (i.e. 0xFFFFFFFF) as
+	 * invalid device?
+	 */
 	typedef uint32 DeviceHandle;
 
 	enum DeviceStringType {