Wrap with let: apply to unsafe qualified expression

#KT-18125 Fixed

idea/testData/quickfix/wrapWithSafeLetCall/unsafeForNullableParameter.kt

@@ -0,0 +1,12 @@
+// "Wrap with '?.let { ... }' call" "false"
+// ACTION: Add 's =' to argument
+// ACTION: Add non-null asserted (!!) call
+// ACTION: Replace with safe (?.) call
+// ACTION: Surround with null check
+// DISABLE-ERRORS
+// WITH_RUNTIME
+fun foo(s: String?) {}
+
+fun bar(s: String?) {
+    foo(s<caret>.substring(1))
+}