[SPARK-21726][SQL][FOLLOW-UP] Check for structural integrity of the plan in Optimzer in test mode

## What changes were proposed in this pull request?

The condition in `Optimizer.isPlanIntegral` is wrong. We should always return `true` if not in test mode.

## How was this patch tested?

Manually test.

Author: Liang-Chi Hsieh <viirya@gmail.com>

Closes #19161 from viirya/SPARK-21726-followup.

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala

@@ -41,7 +41,7 @@ abstract class Optimizer(sessionCatalog: SessionCatalog)
   // Check for structural integrity of the plan in test mode. Currently we only check if a plan is
   // still resolved after the execution of each rule.
   override protected def isPlanIntegral(plan: LogicalPlan): Boolean = {
-    Utils.isTesting && plan.resolved
+    !Utils.isTesting || plan.resolved
   }
 
   protected def fixedPoint = FixedPoint(SQLConf.get.optimizerMaxIterations)