Ensure method call with non-null type

This patch fixes an assert when accessing context information about
a component that has a base class with empty type. Such situations
may occur when the corresponding qmltypes files are not correctly
loaded.

Reviewers: brauch, kfunk, KDevelop

Reviewed By: kfunk, KDevelop

Subscribers: kdevelop-devel

Differential Revision: https://phabricator.kde.org/D1618