[FIR] Fix FirExpressionWithSmartcastImpl.acceptChildren

compiler/fir/tree/src/org/jetbrains/kotlin/fir/expressions/impl/FirExpressionWithSmartcastImpl.kt

@@ -44,7 +44,7 @@ internal class FirExpressionWithSmartcastImpl(
     }
 
     override fun <R, D> acceptChildren(visitor: FirVisitor<R, D>, data: D) {
-        originalExpression.acceptChildren(visitor, data)
+        originalExpression.accept(visitor, data)
     }
 
     override fun <D> transformCalleeReference(transformer: FirTransformer<D>, data: D): FirExpressionWithSmartcast {

compiler/tests-common-new/tests/org/jetbrains/kotlin/test/frontend/fir/handlers/FirDiagnosticsHandler.kt

@@ -146,8 +146,11 @@ class FirDiagnosticsHandler(testServices: TestServices) : FirAnalysisHandler(tes
                         )
                     )
                 }
-
-                element.acceptChildren(this)
+                if (element is FirExpressionWithSmartcast) {
+                    element.originalExpression.acceptChildren(this)
+                } else {
+                    element.acceptChildren(this)
+                }
             }
 
             override fun visitFunctionCall(functionCall: FirFunctionCall) {