Fix path in read errors while writing (#2599)

Author: sampsyo

beets/library.py

@@ -615,7 +615,7 @@ def write(self, path=None, tags=None):
             mediafile = MediaFile(syspath(path),
                                   id3v23=beets.config['id3v23'].get(bool))
         except UnreadableFileError as exc:
-            raise ReadError(self.path, exc)
+            raise ReadError(path, exc)
 
         # Write the tags to the file.
         mediafile.update(item_tags)