trackdb: Retry saving if something goes wrong

Occasionally we have a problem with tags changing during pickling. If
this happens, reschedule the save for later and hope it doesn't happen
again

Signed-off-by: Anna Schumaker <Anna@NoWheyCreamery.com>

trackdb/__init__.py

@@ -63,8 +63,11 @@ Library = LibraryStore()
 
 
 def _do_save():
-    with lib.data.DataFile(File, lib.data.WRITE) as f:
-            f.pickle([ tags.get_state(), Tracks, Library ])
+    try:
+        with lib.data.DataFile(File, lib.data.WRITE) as f:
+                f.pickle([ tags.get_state(), Tracks, Library ])
+    except Exception as e:
+        return lib.bus.RETRY
 
 def save(*args):
     Bus.board(_do_save)