"Replace if with when": do not add empty else block #KT-18681 Fixed

idea/testData/intentions/branched/ifWhen/ifToWhen/ifThenReturn.kt

@@ -0,0 +1,8 @@
+fun test(a: Any, b: Boolean): Int  {
+    when (a) {
+        is Int -> {
+            <caret>if (b) return 1
+        }
+    }
+    return 0
+}

idea/testData/intentions/branched/ifWhen/ifToWhen/ifThenReturn.kt.after

@@ -0,0 +1,10 @@
+fun test(a: Any, b: Boolean): Int  {
+    when (a) {
+        is Int -> {
+            when {
+                b -> return 1
+            }
+        }
+    }
+    return 0
+}