Insert brackets in "Convert reference to lambda" if necessary

So #KT-16394 Fixed

idea/testData/intentions/convertReferenceToLambda/when4.kt

@@ -0,0 +1,10 @@
+class Test {
+    fun bar(a: String) = 1
+
+    fun test(x: Int) {
+        val foo: (a: String) -> Int = when (x) {
+            1 -> <caret>this::bar
+            else -> this::bar
+        }
+    }
+}