Fixed bug in MergeWhenIntention

idea/testData/intentions/branched/when/merge/mergeWithVarSubject.kt

@@ -0,0 +1,16 @@
+// IS_APPLICABLE: false
+fun doSomething<T>(a: T) {}
+
+fun test() {
+    var n = 0
+
+    <caret>when (n) {
+        1 -> n = 2
+        2 -> n = 1
+    }
+
+    when (n) {
+        1 -> doSomething("A")
+        2 -> doSomething("B")
+    }
+}