Stop saving extra drafts!

We only need to call saveifneeded if the activity is exiting
to perform the auto-save of a draft when pressing back/up

Also, whether or not things have changed, if the draft is totally blank,
don't save it

Fixes b/6516255 Empty message is saved as Draft when file is too large to attach

Change-Id: Id746beb1e2543bd4ba63295f88e447407074f626
1 file changed