gitignore: Ignore generated tmpl dir in public docs
clip: Do not modify the special all-clipped cairo_clip_t

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=75819
clip: Fix handling of special all-clipped cairo_clip_t

_cairo_clip_intersect_box() wasn't checking if it was called with the special,
read-only all-clipped clip and thus could have ended up writing to read-only
memory.

References: https://bugs.freedesktop.org/show_bug.cgi?id=75819
Signed-off-by: Uli Schlachter <psychon@znc.in>