Fix queue slice count action (#8550)

## What changed?
- Revert the removal of slice count check in multi-cursor slice count
action.
- The check was incorrectly removed in [#8416
L117](https://github.com/temporalio/temporal/pull/8416/files#diff-deecce1e374d8c4db074d9c923c2b80d1b8e28cef778202aa01397e8d56e1bafL117)

## Why?
- Without the check, the code will panic later in
`pickCompactCandidates` when currentSliceCount < targetSliceCount.

## How did you test it?
- [x] built
- [ ] run locally and tested manually
- [ ] covered by existing tests
- [ ] added new unit test(s)
- [ ] added new functional test(s)
- [x] will follow up with a test PR

Author: yycptt

service/history/queues/action_slice_count.go

@@ -116,6 +116,10 @@ func (a *actionSliceCount) findAndCompactLowSliceCount(
 	targetSliceCount int,
 ) bool {
 	currentSliceCount := a.monitor.GetTotalSliceCount()
+	if currentSliceCount <= targetSliceCount {
+		return true
+	}
+
 	candidates := make([]compactCandidate, 0, currentSliceCount)
 	for readerID, reader := range readers {
 		if !readerPredicate(readerID) {