Support codegen of empty do-while-loop

#KT-3009 In Progress

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

@@ -465,7 +465,10 @@ public class ExpressionCodegen extends JetVisitor<StackValue, StackValue> implem
             conditionValue = generateBlock(statements, true);
         }
         else {
-            gen(body, Type.VOID_TYPE);
+            if (body != null) {
+                gen(body, Type.VOID_TYPE);
+            }
+
             conditionValue = gen(condition);
         }
 

compiler/testData/codegen/box/controlStructures/emptyDoWhile.kt

@@ -0,0 +1,9 @@
+fun box(): String {
+    do while (false);
+
+    var x = 0
+    do while (x++<5);
+    if (x != 6) return "Fail: $x"
+
+    return "OK"
+}

compiler/tests/org/jetbrains/jet/codegen/generated/BlackBoxCodegenTestGenerated.java

@@ -1427,6 +1427,11 @@ public class BlackBoxCodegenTestGenerated extends AbstractBlackBoxCodegenTest {
             doTest("compiler/testData/codegen/box/controlStructures/doWhileFib.kt");
         }
         
+        @TestMetadata("emptyDoWhile.kt")
+        public void testEmptyDoWhile() throws Exception {
+            doTest("compiler/testData/codegen/box/controlStructures/emptyDoWhile.kt");
+        }
+        
         @TestMetadata("emptyIf.kt")
         public void testEmptyIf() throws Exception {
             doTest("compiler/testData/codegen/box/controlStructures/emptyIf.kt");