Manual testing - persistent GL Series in openglseriestest

In the manual test openglseriestest, a GL series can persist after removal until all series have been removed. This happens only if the first series added was a regular series. In this case, the first GL series created will persist in a frozen state until the first series has been removed. If the application window is resized, the persistent GL series will disappear.

Steps to reproduce:

This behavior is seen easily with the theme "dark", green color, and series thickness of 4.

1. Left-click "Add Series".
2. Left-click "Add Series" again an arbitrary amount of times.
3. Left-click "Add GL Series". Remember which series this is.
4. Left-click either "Add Series" or "Add GL Series" an arbitrary amount of times.
5. Left-click "Remove" until only the first series remains. Notice that the first "GL Series" is still visible in a frozen state.

Expected behavior:

Left-clicking "Remove" should completely remove any series.

Observed behavior:

If the first series created was a regular series, then the first GL series created after that will persist after removal until the first series has been removed.

In the image below, GL_4 will persist until Raster_0 has been removed.