This can apparently happen when interrupting a build; reproducible with
"touch workdir/*/UnpackedTarget/*openssl* && make openssl".

The -f parameter would apparently silently ignore some mal-formed
patches but at least it rejects potentially reversed ones,
which causes the "error handler" in gb_UnpackedTarball__command
to touch the "prepare" target so the next make is successful.

Change-Id: I7bbd7d9385d990a69214a3a2d9bb20b5a7173748