Fix for bug #950287

1. When sending local changes to Evernote, skip an item in the pending
queue if it is not found in the local db. This happens when a new note
is opened and then canceled.

2. When sendChanges is called (to send local changes to Evernote), if
pending queues are empty, don't start the processing.

3. Variable 'totalQueueChunks', used to compute progress, can be zero.
Added defensive code to avoid divide by zero error.
Merge pull request #1 from yor-mozilla-com/fix950287

Fix for bug #950287