libkmod: clear file->memory if map fails

libkmod: clear file->memory if map fails

On mmap failure file->memory is set to -1, which we'll happily pass down
to munmap later on.

More importantly, since we do a NULL check in kmod_file_load_contents()
we will exit the function without (re)attempting the load again.

Since we ignore the return code for the load function(s), one can end up
calling kmod_elf_get_memory() and feed that -1 into init_module.

Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Lucas De Marchi <lucas.de.marchi@gmail.com>