[library] RSS - reuse db file id when performing meta scan

Fixes issue when performing an 'api/rescan' (results in RSS_SCAN_META scan type
in this module) that would result in a library_media_save() -> a readd even for
entries that already exist in db.  This would result in dropping db record, incl
play_count etc instead of an update

src/library/rssscanner.c

@@ -453,6 +453,13 @@ rss_save(struct playlist_info *pli, int *count, enum rss_scan_type scan_type)
 	  if (ret > 0)
 	    continue;
 	}
+      else if (scan_type == RSS_SCAN_META)
+	{
+	  // Using existing file id if already in library, resulting in update but preserving play_count etc
+	  mfi.id = db_file_id_bypath(ri.url);
+	  if (mfi.id > 0)
+	    time_added = 0;
+	}
 
       scan_metadata_stream(&mfi, ri.url);