libkmod: check for trailing \0 in __ksymtab_strings

libkmod: check for trailing \0 in __ksymtab_strings

As per the documentation (man 5 elf) the section must be null
terminated. Move the check further up and remove the no longer needed
code trying to workaround non-compliant instances.

Note: drop the erroneous +1 in the overflow (malloc size) calculation

Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Reviewed-by: Tobias Stoeckmann <tobias@stoeckmann.org>
Link: https://github.com/kmod-project/kmod/pull/210
Signed-off-by: Lucas De Marchi <lucas.de.marchi@gmail.com>