Remove braces: add parentheses to if-else in more general case

Related to KT-18308

idea/testData/intentions/removeBraces/elseInPlusAssignExpression.kt.after

@@ -0,0 +1,7 @@
+// WITH_RUNTIME
+fun test(b: Boolean) {
+    val list1 = mutableListOf(1)
+    val list2 = mutableListOf(2)
+
+    (if (b) {list1} else list2) += 3
+}