The previous code assumed that `initFrame` during the `new_frame` state would always result in the `in_frame` state, but that's not always the case. `initFrame` can also result in the `skippable_frame` state, which would lead to access of union field 'in_frame' while field 'skipping_frame' is active.
Now, the switch is re-entered with the updated state so either case is handled appropriately.
Fixes the crashes from https://github.com/ziglang/zig/issues/24817
Previously, the "allow EndOfStream" part of this logic was too permissive. If there are a few dangling bytes at the end of the stream, that should be treated as a bad magic number. The only case where EndOfStream is allowed is when the stream is truly at the end, with exactly zero bytes available.
This passes tests but it doesn't provide as big a window size as is
required to decompress larger streams.
The next commit in this branch will work towards that, without
introducing an additional buffer.
