Keep insert symbol on axis enabled when library thumbail is locked.

Details: <p>Testing:</p><p>- Select a symbol from library and lock it by double-clicking it.</p><p>- Activate &#39;Insert symbol on axis&#39;</p><p>- Insert some symbols on axis across some connections.</p><p>- If &#39;Insert&nbsp;symbol on axis&#39; is still active after symbol insertion, we&#39;re good.</p>