add a dummy GfxState to Page::loadThumb for proper color space handling

As far as I can tell this was the only remaining spot in the code where
GfxColorSpace::parse was called without a properly initialized GfxState.
6 jobs for cleanup_displayprofile_init in 4 minutes and 50 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #2795568
build

00:04:50

passed #2795573
build_android

00:00:35

passed #2795569
build_clang_libcpp

00:03:07

passed #2795572
build_clazy

00:02:02

passed #2795571
build_mingw64_fedora

00:02:27

passed #2795570
build_ubuntu_16_04

00:01:24