libelf: Always set ELF maxsize when reading an ELF file for sanity checks.

libelf: Always set ELF maxsize when reading an ELF file for sanity checks.

There are various sanity checks that depend on knowing the file size
of the underlying ELF file which we only used when mmapping the ELF file.
Although we probably won't crash if we use pread to try to read from
the file, we still might return completely bogus data structures. This
could cause us to malloc insane amounts of memory.

Always try to get the maxsize when unknown in elf_begin.c (read_file).

https://bugzilla.redhat.com/show_bug.cgi?id=1388057

Signed-off-by: Mark Wielaard <mjw@redhat.com>