Add context to stdHtml on Overview._renderPage() for use in gui_hooks

[Shirajuki]

Description

As of now the hooks of webview_will_set_content for instance, returns a context of type None after navigating to the Overview webview. Adding the line of 140 would simply fix this bug.

Checklist:

Please replace the space inside the brackets with an x and fill out the ellipses if the following items apply:

• [x] I've read and understood the contribution guidelines
• [x] I've tested my changes against at least one of the following Anki builds:
  • [x] Latest standard Anki 2.1 binary build
  • [ ] Latest alternative Anki 2.1 binary build
• [x] I've tested my changes on at least one of the following platforms:
  • [ ] Linux, version:
  • [x] Windows, version:
  • [ ] macOS, version:
• [ ] My changes potentially affect non-desktop platforms, of which I've tested:
  • [ ] AnkiMobile, version:
  • [ ] AnkiDroid, version:
  • [ ] AnkiWeb

[glutanimate]

Hey Shirajuki, appreciate the contribution! This code path is no longer in the latest version of the add-on as I decided to drop support for Anki versions below 2.1.28. Still, I do appreciate the thoughtful PR. Thank you!