don't push new URL into engine in the CurrentMetadataChanged slot - send it the beginning and end markers only

this means that Clementine still skips broken songs while at the same time fixes issue #1565

src/core/player.cpp

@@ -277,8 +277,7 @@ void Player::PlayAt(int index, Engine::TrackChangeType change, bool reshuffle) {
 void Player::CurrentMetadataChanged(const Song& metadata) {
   // those things might have changed (especially when a previously invalid
   // song was reloaded) so we push the latest version into Engine
-  engine_->Load(metadata.url(), Engine::Auto,
-                metadata.beginning_nanosec(), metadata.end_nanosec());
+  engine_->RefreshMarkers(metadata.beginning_nanosec(), metadata.end_nanosec());
 
 #ifdef HAVE_LIBLASTFM
   lastfm_->NowPlaying(metadata);

src/engines/enginebase.h

@@ -64,6 +64,13 @@ class Base : public QObject, boost::noncopyable {
   // in miliseconds.
   virtual bool Load(const QUrl& url, TrackChangeType change,
                     quint64 beginning_nanosec, qint64 end_nanosec);
+  // Sets new values for the beginning and end markers of the currently playing
+  // song.
+  // This doesn't change the state of engine or the stream's current position.
+  virtual void RefreshMarkers(quint64 beginning_nanosec, qint64 end_nanosec) {
+    beginning_nanosec_ = beginning_nanosec;
+    end_nanosec_ = end_nanosec;
+  }
 
   // Plays a media stream represented with the URL 'u' from the given 'beginning'
   // to the given 'end' (usually from 0 to a song's length). Both markers