imap: create copy of uids to retain sort order

Commit fdfec2c07a seqmap: refactor seqmap to use slice instead of map
introduced a regression to imap sorting (if supported). The slice passed
to seqmap was being sorted in place by UID, thus breaking any sort order
sent by the server.

Create a copy of the slice to retain the sort order reported to the UI
while also keeping a correct map for seqnum -> UID in the worker.

Signed-off-by: Tim Culverhouse <tim@timculverhouse.com>
Acked-by: Robin Jarry <robin@jarry.cc>

worker/imap/seqmap_test.go

@@ -22,8 +22,11 @@ func TestSeqMap(t *testing.T) {
 	_, found = seqmap.Pop(0)
 	assert.Equal(false, found)
 
-	seqmap.Initialize([]uint32{1337, 42, 1107})
+	uids := []uint32{1337, 42, 1107}
+	seqmap.Initialize(uids)
 	assert.Equal(3, seqmap.Size())
+	// Original list should remain unsorted
+	assert.Equal([]uint32{1337, 42, 1107}, uids)
 
 	_, found = seqmap.Pop(0)
 	assert.Equal(false, found)