KT-723 optional boxing after call to .inc()

compiler/backend/src/org/jetbrains/jet/codegen/ExpressionCodegen.java

@@ -2159,8 +2159,10 @@ public class ExpressionCodegen extends JetVisitor<StackValue, StackValue> {
                         case -1:
                             throw new UnsupportedOperationException();
                     }
-                            
-                    ((CallableMethod)callable).invoke(v);
+
+                    CallableMethod callableMethod = (CallableMethod) callable;
+                    callableMethod.invoke(v);
+                    StackValue.onStack(callableMethod.getSignature().getAsmMethod().getReturnType()).put(value.type, v);
                     value.store(v);
                     return StackValue.onStack(type);
                 }

compiler/testData/codegen/regressions/kt723.kt

@@ -0,0 +1,8 @@
+fun Int?.inc() : Int { if (this != null) return this.inc() else throw NullPointerException() }
+
+public fun box() : String {
+    var i : Int? = 10
+    val j = i++
+
+    return if(j==10 && 11 == i) "OK" else "fail"
+}

compiler/tests/org/jetbrains/jet/codegen/ClassGenTest.java

@@ -285,4 +285,8 @@ public class ClassGenTest extends CodegenTestCase {
     public void testKt1213() throws Exception {
 //        blackBoxFile("regressions/kt1213.kt");
     }
+
+    public void testKt723() throws Exception {
+        blackBoxFile("regressions/kt723.kt");
+    }
 }