Fix codegen of do-while condition

The condition of a do-while loop can use variables declared in the loop
(variables can only be declared inside a block). Previously this behaviour
caused crash because after the block was generated, all variables declared
inside that block were gone from myFrameMap

 #KT-3280 Fixed

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

@@ -0,0 +1,15 @@
+fun box(): String {
+    var x = 0
+    do x++ while (x < 5)
+    if (x != 5) return "Fail 1 $x"
+    
+    var y = 0
+    do { y++ } while (y < 5)
+    if (y != 5) return "Fail 2 $y"
+    
+    var z = ""
+    do { z += z.length } while (z.length < 5)
+    if (z != "01234") return "Fail 3 $z"
+    
+    return "OK"
+}