Do not retrieve parent of FQname for root

#KT-8642 Fixed

compiler/testData/diagnostics/testsWithStdLib/purelyImplementedCollection/invalidFqName.kt

@@ -0,0 +1,29 @@
+// !DIAGNOSTICS: -UNUSED_VARIABLE
+
+// FILE: A.java
+import java.util.*
+
+@kotlin.jvm.PurelyImplements("")
+public class A<T> extends AbstractList<T> {
+    @Override
+    public T get(int index) {
+        return null;
+    }
+
+    @Override
+    public int size() {
+        return 0;
+    }
+
+    static A rawField = null;
+}
+
+// FILE: B.java
+import java.util.*
+
+@kotlin.jvm.PurelyImplements("[INVALID]")
+public class B<T> extends AbstractList<T> {}
+
+// FILE: main.kt
+val x = A<String>()
+val y = B<String>()