## Summary
* Unset openEpubPath on boot and set once epub fully loaded
## Additional Context
* If an epub was crashing when loading, it was possible to get the
device stuck into a loop. There was no way to get back to the home
screen as we'd always load you back into old epub
* Break this loop by clearing the stored value when we boot, still
jumping to the last open epub, but only resetting that value once the
epub has been fully loaded
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