x11-wm/compiz: Fix compiz-manager texture size parsing error

compiz-manager doesn't cover the possibility of duplicate output from
glxinfo at line 238, which causes check_texture_size() to fail. Let's fix
it by limiting the number of output lines to 1.

PR: 247476
Submitted by: Vladimir Bychik
Approved by: maintainer (Chris Hutchinson)
MFH: 2020Q4