Fix: Strip the prefix of the path
Fix: Strip the prefix of the path

The previous implementation did not strip the prefix of the "relpath"
header value, which resulted in the whole path being in the header,
which is obviously wrong.

Signed-off-by: Matthias Beyer <1d6e1cf70ec6f9ab28d3ea4b27a49a77654d370e@beyermatthias.de>

matthiasbeyer/imag,matthiasbeyer/imag