AudioManager: if alc.openDevice() returns null, don't call alc.createContext() to avoid a SIGNAL 11 crash

src/lime/media/AudioManager.hx

@@ -34,10 +34,13 @@ class AudioManager
 					var alc = context.openal;
 
 					var device = alc.openDevice();
+					if (device != null)
+					{
 						var ctx = alc.createContext(device);
 						alc.makeContextCurrent(ctx);
 						alc.processContext(ctx);
 					}
+				}
 				#end
 			}