FE: properly clear the deferred generator stack

Before this commit the stack wasn't cleared for read variable case.
#KT-47168 Fixed

compiler/tests-gen/org/jetbrains/kotlin/codegen/LightAnalysisModeTestGenerated.java

@@ -5744,6 +5744,11 @@ public class LightAnalysisModeTestGenerated extends AbstractLightAnalysisModeTes
             runTest("compiler/testData/codegen/box/contracts/kt45236.kt");
         }
 
+        @TestMetadata("kt47168.kt")
+        public void testKt47168() throws Exception {
+            runTest("compiler/testData/codegen/box/contracts/kt47168.kt");
+        }
+
         @TestMetadata("lambdaParameter.kt")
         public void testLambdaParameter() throws Exception {
             runTest("compiler/testData/codegen/box/contracts/lambdaParameter.kt");