Apparently IMAP servers may return multiple SEARCH responses for a
single SEARCH command, and we need to handle all of them.
Before the IMAP rework there was 3 methods that issued the SEARCH command.
Two of them ware doing it right, but the other wasn't, which was what
I copied from, unfortunately!
In case you're wondering, originally the test for this method was done through
upper methods, e.g. getMessage().
Bug 2911647
Backport of Ia50072944d5b01c1e59541c3a966067b13910cc4
Change-Id: Iab5d3fa21e403f2e1043990112154fbb72322b02
29f0638f4d