[lldb] Fix missing return in NativeFile::SeekFromEnd stream path (#188596)
The stream path in NativeFile::SeekFromEnd was missing a `return result`
statement after the fseek block, causing it to fall through to the error
handler which overwrites the error status with "invalid file handle"
even on success. Both SeekFromStart and SeekFromCurrent correctly return
after their stream blocks.
while no active callers to this function, It is still worth fixing this.