Check for rev with invalid JSON in CBLRestPusher
Check for rev with invalid JSON in CBLRestPusher

It shouldn't be possible for invalid JSON to end up in the database,
but from issue #1179 it seems to have happened. This adds a check for it
because if it isn't caught at this point, it creates trouble a bit
later when the pusher tries to prepare the dictionary to upload.

Fixes #1179 (I think)

brendand/couchbase-lite-ios,amco/couchbase-lite-ios,couchbase/couchbase-lite-ios,brendand/couchbase-lite-ios,amco/couchbase-lite-ios,amco/couchbase-lite-ios,couchbase/couchbase-lite-ios,amco/couchbase-lite-ios,couchbase/couchbase-lite-ios,amco/couchbase-lite-ios,brendand/couchbase-lite-ios,couchbase/couchbase-lite-ios,amco/couchbase-lite-ios,brendand/couchbase-lite-ios,couchbase/couchbase-lite-ios,amco/couchbase-lite-ios,couchbase/couchbase-lite-ios,brendand/couchbase-lite-ios