VLCMedia: fix abort from dealloc when init failed

There are numerous reason to fail from the init, alloc fail, url invalid UTF8
parsing error. In that case, events were not attached from the init method but
were still dettached from dealloc.

(cherry picked from commit 22d316bbec59637283a49cba9c303289bcdabecc)

Sources/VLCMedia.m

@@ -123,6 +123,7 @@ void close_cb(void *opaque) {
     BOOL                    isArtFetched;           ///< Value used to determine of the artwork has been parsed
     BOOL                    areOthersMetaFetched;   ///< Value used to determine of the other meta has been parsed
     BOOL                    isArtURLFetched;        ///< Value used to determine of the other meta has been preparsed
+    BOOL                    eventsAttached;         ///< YES when events are attached
     NSMutableDictionary     *_metaDictionary;       ///< Dictionary to cache metadata read from libvlc
     NSInputStream           *stream;                ///< Stream object if instance is initialized via NSInputStream to pass to callbacks
 }
@@ -314,18 +315,22 @@ static void HandleMediaParsedChanged(const libvlc_event_t * event, void * self)
 
 - (void)dealloc
 {
-    libvlc_event_manager_t * p_em = libvlc_media_event_manager(p_md);
-    if (p_em) {
-        libvlc_event_detach(p_em, libvlc_MediaMetaChanged,     HandleMediaMetaChanged,     (__bridge void *)(self));
-        libvlc_event_detach(p_em, libvlc_MediaDurationChanged, HandleMediaDurationChanged, (__bridge void *)(self));
-        libvlc_event_detach(p_em, libvlc_MediaStateChanged,    HandleMediaStateChanged,    (__bridge void *)(self));
-        libvlc_event_detach(p_em, libvlc_MediaSubItemAdded,    HandleMediaSubItemAdded,    (__bridge void *)(self));
-        libvlc_event_detach(p_em, libvlc_MediaParsedChanged,    HandleMediaParsedChanged,   (__bridge void *)(self));
+    if (eventsAttached)
+    {
+        libvlc_event_manager_t * p_em = libvlc_media_event_manager(p_md);
+        if (p_em) {
+            libvlc_event_detach(p_em, libvlc_MediaMetaChanged,     HandleMediaMetaChanged,     (__bridge void *)(self));
+            libvlc_event_detach(p_em, libvlc_MediaDurationChanged, HandleMediaDurationChanged, (__bridge void *)(self));
+            libvlc_event_detach(p_em, libvlc_MediaStateChanged,    HandleMediaStateChanged,    (__bridge void *)(self));
+            libvlc_event_detach(p_em, libvlc_MediaSubItemAdded,    HandleMediaSubItemAdded,    (__bridge void *)(self));
+            libvlc_event_detach(p_em, libvlc_MediaParsedChanged,    HandleMediaParsedChanged,   (__bridge void *)(self));
+        }
     }
 
     [[VLCEventManager sharedManager] cancelCallToObject:self];
 
-    libvlc_media_release( p_md );
+    if (p_md)
+        libvlc_media_release(p_md);
 }
 
 - (VLCMediaType)mediaType
@@ -984,6 +989,7 @@ NSString *const VLCMediaTracksInformationTextEncoding = @"encoding"; // NSString
         libvlc_event_attach(p_em, libvlc_MediaStateChanged,    HandleMediaStateChanged,    (__bridge void *)(self));
         libvlc_event_attach(p_em, libvlc_MediaSubItemAdded,    HandleMediaSubItemAdded,    (__bridge void *)(self));
         libvlc_event_attach(p_em, libvlc_MediaParsedChanged,    HandleMediaParsedChanged,   (__bridge void *)(self));
+        eventsAttached = YES;
     }
 
     libvlc_media_list_t * p_mlist = libvlc_media_subitems( p_md );