Don't reject updates to malformed events

We want to prevent apps from inserting bad data into the database,
but we need to be a bit more lenient when the bad data is already
present.  When processing an update, we now only validate the merged
data if the original event looks okay.

Bug 5173841

Change-Id: Id5ec755eb0d8ef6e96a9d67857b4c5dbb2ef4741
1 file changed