Fix conversion of assignment as expression in J2K

Blockless if's and so with assignment as expression inside
should turn into blockful
 #KT-16816 fixed

j2k/testData/fileOrElement/for/assignmentAsExpressionInBody.kt

@@ -0,0 +1,10 @@
+class SomeClass {
+    internal fun doSomeFor() {
+        var a: Int
+        var b: Int
+        for (i in 0..9) {
+            b = i
+            a = b
+        }
+    }
+}