Fix crashes / bad errors when loading a file fails.

Core/Loaders.cpp

@@ -124,6 +124,7 @@ bool LoadFile(const char *filename, std::string *error_string)
 	case FILETYPE_UNKNOWN:
 	default:
 		ERROR_LOG(LOADER, "Failed to identify file");
+		*error_string = "Failed to identify file";
 		break;
 	}
 	return false;

Windows/DSoundStream.cpp

@@ -14,8 +14,8 @@ namespace DSound
 
 	StreamCallback callback;
 
-	IDirectSound8 *ds;
-	IDirectSoundBuffer *dsBuffer;
+	IDirectSound8 *ds = NULL;
+	IDirectSoundBuffer *dsBuffer = NULL;
 
 	int bufferSize; // bytes
 	int totalRenderedBytes;
@@ -196,8 +196,10 @@ namespace DSound
 		/*
 		while (threadData!=2)
 			;*/
-		dsBuffer->Release();
-		ds->Release();
+		if (dsBuffer != NULL)
+			dsBuffer->Release();
+		if (ds != NULL)
+			ds->Release();
 
 		CloseHandle(soundSyncEvent);
 	}

Windows/WindowsHost.cpp

@@ -97,7 +97,8 @@ void WindowsHost::UpdateSound()
 void WindowsHost::ShutdownSound()
 {
 	DSound::DSound_StopSound();
-	delete curMixer;
+	if (curMixer != NULL)
+		delete curMixer;
 	curMixer = 0;
 }