libxbps: make xbps_find_virtualpkg_user *only* look for virtual pkgs.
libxbps: make xbps_find_virtualpkg_user *only* look for virtual pkgs.

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