core: fix missing imports for anonymous classes

jadx-core/src/main/java/jadx/core/codegen/ClassGen.java

@@ -463,7 +463,7 @@ public class ClassGen {
 	}
 
 	public ClassGen getParentGen() {
-		return parentGen;
+		return parentGen == null ? this : parentGen;
 	}
 
 	public AnnotationGen getAnnotationGen() {