Convert to expression body: take nested whens into account

idea/testData/intentions/convertToExpressionBody/ifWhenUnitNonExhaustive.kt

@@ -0,0 +1,18 @@
+// IS_APPLICABLE: false
+enum class AccessMode { READ, WRITE, RW }
+fun whenExpr(mode: Boolean, access: AccessMode) {
+    <caret>if (mode) {
+        when (access) {
+            AccessMode.READ -> println("read")
+            AccessMode.WRITE -> println("write")
+        }
+    }
+    else {
+        when (access) {
+            AccessMode.READ -> println("noread")
+            AccessMode.WRITE -> println("nowrite")
+            AccessMode.RW -> println("no both")
+        }
+    }
+}
+fun println(s: String) {}