libdl: fix problem with unmapping
libdl: fix problem with unmapping

The munmap was still called with broken length, as sometimes
start was empty. This finally solves segfaults when running
php -m with ldap module activated.

kraj/uclibc-ng,kraj/uclibc-ng,kraj/uclibc-ng,wbx-github/uclibc-ng,kraj/uclibc-ng,wbx-github/uclibc-ng,wbx-github/uclibc-ng,wbx-github/uclibc-ng