Taglib: do not write 0 as track position if tracknumber is ""

(cherry picked from commit ea81feee5bf176e15347baf9761ba9525e5a3040)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

modules/meta_engine/taglib.cpp

@@ -630,11 +630,11 @@ static int WriteMeta( vlc_object_t *p_this )
 #undef SET
 
     psz_meta = input_item_GetDate( p_item );
-    if( psz_meta ) p_tag->setYear( atoi( psz_meta ) );
+    if( !EMPTY_STR(psz_meta) ) p_tag->setYear( atoi( psz_meta ) );
     free( psz_meta );
 
     psz_meta = input_item_GetTrackNum( p_item );
-    if( psz_meta ) p_tag->setTrack( atoi( psz_meta ) );
+    if( !EMPTY_STR(psz_meta) ) p_tag->setTrack( atoi( psz_meta ) );
     free( psz_meta );