[IR BE] Fix capturing of var-locals inside class/field initializers

compiler/testData/codegen/box/callableReference/bound/captureVarInInitBlock.kt

@@ -0,0 +1,20 @@
+
+fun bar(b: ()-> Unit) { b() }
+
+class C() {
+    var f: Int
+
+    init {
+        var i = 10
+        bar {
+            i = 20
+        }
+        f = i + 1
+    }
+}
+
+fun box(): String {
+    val c = C()
+    if (c.f != 21) return "fail"
+    return "OK"
+}