IMedia: Constify labels() accessor

include/medialibrary/IMedia.h

@@ -121,7 +121,7 @@ class IMedia
         virtual bool addLabel( LabelPtr label ) = 0;
         virtual bool removeLabel( LabelPtr label ) = 0;
         virtual MoviePtr movie() const = 0;
-        virtual Query<ILabel> labels() = 0;
+        virtual Query<ILabel> labels() const = 0;
         virtual Query<IVideoTrack> videoTracks() = 0;
         virtual Query<IAudioTrack> audioTracks() = 0;
         ///

src/Media.cpp

@@ -162,7 +162,7 @@ void Media::setShowEpisode( ShowEpisodePtr episode )
     m_changed = true;
 }
 
-Query<ILabel> Media::labels()
+Query<ILabel> Media::labels() const
 {
     static const std::string req = "FROM " + policy::LabelTable::Name + " l "
             "INNER JOIN LabelFileRelation lfr ON lfr.label_id = l.id_label "

src/Media.h

@@ -109,7 +109,7 @@ class Media : public IMedia, public DatabaseHelpers<Media, policy::MediaTable>
         void setShowEpisode( ShowEpisodePtr episode );
         virtual bool addLabel( LabelPtr label ) override;
         virtual bool removeLabel( LabelPtr label ) override;
-        virtual Query<ILabel> labels() override;
+        virtual Query<ILabel> labels() const override;
         virtual int playCount() const  override;
         virtual bool increasePlayCount() override;
         virtual bool isFavorite() const override;