unstrip: Add sanity check for bogus sh_offset of allocated sections.

unstrip: Add sanity check for bogus sh_offset of allocated sections.

unstrip tries to preserve any allocated section offset in an
executable or shared library. If the offset is extremely large that
would cause the disk to fill up because we will write out a file with
lots of padding to put the section contents at that particular
offset. Add a sanity check that makes sure we just error out if there
is such a bogus offset by checking that no offset is larger than the
original ELF file size.

https://sourceware.org/bugzilla/show_bug.cgi?id=25083

Signed-off-by: Mark Wielaard <mark@klomp.org>