"Wrap with let": fix for nullable extension function call #KT-6364 Fixed

idea/testData/quickfix/wrapWithSafeLetCall/extentionFunctionCall2.kt

@@ -0,0 +1,10 @@
+// "Wrap with '?.let { ... }' call" "true"
+// WITH_RUNTIME
+
+fun f(s: String, action: (String.() -> Unit)?) {
+    s.foo().bar().action<caret>()
+}
+
+fun String.foo() = ""
+
+fun String.bar() = ""