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

idea/testData/intentions/convertToExpressionBody/lambdaIfUnit.kt.after

@@ -0,0 +1,10 @@
+// IS_APPLICABLE: true
+
+fun <T> run(f: () -> T) = f()
+fun whenExpr(flag: Boolean) = run {
+    println("run")
+    if (flag) {
+        println("flag")
+    }
+}
+fun println(s: String) {}