Fix bug in ShortenReferences visitor (do not skip PSI elements after modication)

idea/testData/shortenRefs/classObject.kt

@@ -0,0 +1,16 @@
+package p.q
+
+<selection>fun foo(): Int {
+    p.q.MyClass.foo()
+    return p.q.MyClass.coProp + 10
+}</selection>
+
+class MyClass {
+    class object {
+        val coProp = 1
+
+        fun foo() {
+
+        }
+    }
+}