Only use local max message ID when fetching new messages if it is valid
Only use local max message ID when fetching new messages if it is valid

It's possible that the local message id is -1 if our message polling failed
and we're in the middle of a reset. If we load exactly 1 new message after
this reset, don't use the local max message id for our range pair.

knowcliu/zulip-ios,zulip/zulip-ios,zulip/zulip-ios,knowcliu/zulip-ios