"Remove redundant toString": fix false positive for nested nullable

So #KT-24557 Fixed

idea/src/org/jetbrains/kotlin/idea/intentions/RemoveRedundantCallsOfConversionMethodsIntention.kt

@@ -82,9 +82,11 @@ class RemoveRedundantCallsOfConversionMethodsIntention : SelfTargetingRangeInten
                     Boolean::class.qualifiedName
                 } else {
                     resolvedCall?.candidateDescriptor?.returnType?.let {
-                        if (it.isFlexible()) null
+                        when {
-                        else if (it.isMarkedNullable && parent !is KtSafeQualifiedExpression) null
+                            it.isFlexible() -> null
-                        else it.getFqNameAsString()
+                            parent !is KtSafeQualifiedExpression && (this is KtSafeQualifiedExpression || it.isMarkedNullable) -> null
+                            else -> it.getFqNameAsString()
+                        }
                     }
                 }
             }

idea/testData/intentions/removeRedundantCallsOfConversionMethods/nullable2.kt

@@ -0,0 +1,7 @@
+// IS_APPLICABLE: false
+// WITH_RUNTIME
+data class Foo(val name: String)
+
+fun nullable2(foo: Foo?) {
+    val s: String = foo?.name.toString()<caret>
+}

idea/testData/intentions/removeRedundantCallsOfConversionMethods/safeString2.kt

@@ -0,0 +1,6 @@
+// WITH_RUNTIME
+data class Foo(val name: String)
+
+fun test(foo: Foo?) {
+    val s: String? = foo?.name?.toString()<caret>
+}

idea/testData/intentions/removeRedundantCallsOfConversionMethods/safeString2.kt.after

@@ -0,0 +1,6 @@
+// WITH_RUNTIME
+data class Foo(val name: String)
+
+fun test(foo: Foo?) {
+    val s: String? = foo?.name
+}

idea/tests/org/jetbrains/kotlin/idea/intentions/IntentionTestGenerated.java

@@ -13242,11 +13242,21 @@ public class IntentionTestGenerated extends AbstractIntentionTest {
             runTest("idea/testData/intentions/removeRedundantCallsOfConversionMethods/nullable.kt");
         }
 
+        @TestMetadata("nullable2.kt")
+        public void testNullable2() throws Exception {
+            runTest("idea/testData/intentions/removeRedundantCallsOfConversionMethods/nullable2.kt");
+        }
+
         @TestMetadata("safeString.kt")
         public void testSafeString() throws Exception {
             runTest("idea/testData/intentions/removeRedundantCallsOfConversionMethods/safeString.kt");
         }
 
+        @TestMetadata("safeString2.kt")
+        public void testSafeString2() throws Exception {
+            runTest("idea/testData/intentions/removeRedundantCallsOfConversionMethods/safeString2.kt");
+        }
+
         @TestMetadata("short.kt")
         public void testShort() throws Exception {
             runTest("idea/testData/intentions/removeRedundantCallsOfConversionMethods/short.kt");