fix: [2.5] Fix deactivate balance checker also stops stopping balance (milvus-io#44835)

issue: milvus-io#43858
pr: milvus-io#44834
Fix the issue introduced in PR milvus-io#43992 where deactivating the balance
checker incorrectly stops stopping balance operations.

Changes:
- Move IsActive() check after stopping balance logic
- Only skip normal balance when checker is inactive
- Allow stopping balance to proceed regardless of checker state

This ensures stopping balance can execute even when the balance checker
is deactivated.

---------

Signed-off-by: Wei Liu <[email protected]>

Author: weiliu1031

internal/querycoordv2/checkers/balance_checker.go

@@ -468,11 +468,6 @@ func (b *BalanceChecker) submitTasks(segmentTasks, channelTasks []task.Task) {
 // The method tracks execution time and logs warnings for slow operations
 // to help identify performance bottlenecks in large clusters.
 func (b *BalanceChecker) Check(ctx context.Context) []task.Task {
-	// Skip balance operations if the checker is not active
-	if !b.IsActive() {
-		return nil
-	}
-
 	// Performance monitoring: track execution time
 	start := time.Now()
 	defer func() {
@@ -503,6 +498,11 @@ func (b *BalanceChecker) Check(ctx context.Context) []task.Task {
 		}
 	}
 
+	// Only Skip normal balance operations if the checker is not active
+	if !b.IsActive() {
+		return nil
+	}
+
 	// Phase 2: Process normal balance if no stopping balance was needed
 	// This handles regular load balancing operations for cluster optimization
 	if paramtable.Get().QueryCoordCfg.AutoBalance.GetAsBool() {