Empty or whitespace-only .rockspec files cause parseRockspecBlock to
panic with "index out of range" because the existing end-of-data guard
requires len(out) > 0 before returning the "unexpected end of block"
error, letting the bare data[*i] access on the next line crash.
Split the guard so that:
- partial content at end of data still returns the existing error
- empty data (or whitespace-only) returns an empty block cleanly
Closes#4824.
Signed-off-by: Akihiko Komada <aki1770@gmail.com>
