## Description
When clicking on an episode, the app assumes if there is a season ID for
the episode, then there must be a series ID. However, on my JF 12.0
server, an episode (with no metadata) appeared on my Continue Watching
and it has a season ID (which in turn has a series ID) but no series ID.
I'm not sure if this really a valid situation or if it's a server bug,
but Wholphin shouldn't crash at least. So this PR checks both `seasonId`
and `seriesId` and if either is null, falls back to the generic "Episode
Page". Similarly, if a season has no `seriesId` (again, not sure if a
valid situation), a crash won't occur, however there is no generic
"Season Page", so an error page is shown.
### Related issues
TODO, check JF server issues, maybe fixed in 12.1?
### Testing
Emulator
## Screenshots
N/a
## AI or LLM usage
None
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