Convert to expression body is forbidden for if without else #KT-12951 Fixed

idea/testData/intentions/convertToExpressionBody/whenIfUnitExhaustive.kt

@@ -0,0 +1,10 @@
+// IS_APPLICABLE: true
+enum class AccessMode { READ, WRITE, RW }
+fun whenExpr(mode: Boolean, access: AccessMode) {
+    <caret>when (access) {
+        AccessMode.READ -> if (mode) println("read") else println("noread")
+        AccessMode.WRITE -> if (mode) println("write") else println("nowrite")
+        AccessMode.RW -> if (mode) println("both") else println("no both")
+    }
+}
+fun println(s: String) {}