imapc: Don't process untagged replies in mailbox that isn't fully selected yet

imapc: Don't process untagged replies in mailbox that isn't fully selected yet

For example if the communication was:

C: a SELECT box1
...
C: b SELECT box2
S: * 1 EXPUNGE
S: * 1 EXISTS
S: * OK [UIDVALIDITY 1675948459] UIDs valid
S: ...
S: b OK

The expunge was intended for box1, not box2. This caused:
Warning: imapc(...): Mailbox '...' state corrupted: EXPUNGE received for empty mailbox - reconnecting

Fixed this by ignoring untagged EXPUNGE, FETCH, SEARCH and ESEARCH replies
when the UIDVALIDITY reply hasn't been yet received for a mailbox.