Fixes bug # 2148971
Note, this condition happens when we APPEND a message to the server
but then we turn around and query for it, and the server reports that
it's not there:
>>> 7 APPEND "Sent" {490}
<<< #null# [Ready, for, argument]
<<< #null# [194, EXISTS]
<<< #7# [OK, [APPENDUID, 1233339552, 1191], APPEND, completed]
>>> 8 UID SEARCH (HEADER MESSAGE-ID \
<pwyc0i5yviwvu5nwio2lwdo5.1254073239445@email.android.com>)
<<< #null# [SEARCH]
<<< #8# [OK, UID, SEARCH, completed]
>>> 9 UID SEARCH UID NULL
<<< #9# [BAD, UID, SEARCH, error;, bogus, or, incorrect, syntax, \
of, search, critera]
I don't know why the Yahoo! server did this, but now we'll at least not
crash if they do it again.
ba64cbcaf8