This PR creates a new unknown.svg file in Images List, and uses that when a Book page tries to load a bundle that has artwork that wxUiEditor doesn't know about. This can occur with custom ART providers. Without the replacement bundle, wxWidgets will crash.
This fixes the wxUiEditor side of the crash referred to in #1359 but leaves the issue open because the wxWidgets code needs to be fixed as well.
This PR creates a new unknown.svg file in Images List, and uses that when a Book page tries to load a bundle that has artwork that wxUiEditor doesn't know about. This can occur with custom ART providers. Without the replacement bundle, wxWidgets will crash.
This fixes the wxUiEditor side of the crash referred to in #1359 but leaves the issue open because the wxWidgets code needs to be fixed as well.