xbps_check_is_installed_pkg: fix a leak in error paths reported by valgrind.
xbps_check_is_installed_pkg: fix a leak in error paths reported by valgrind.

--HG--
extra : convert_revision : xtraeme%40gmail.com-20091023091157-h3tlqw2nz67m72ep

ebfe/xbps,datenwolf/xbps,stpx/xbps,datenwolf/xbps,datenwolf/xbps,stpx/xbps,ebfe/xbps,ebfe/xbps,stpx/xbps