Clip from 1025px (which is what this test is about) to 1024px because the
GLES2 renderer in CI otherwise scales its repeat node offscreen for the
--repeat version of this test and that conveniently produces off-by-one
misrenderings everywhere.
However, we need to keep the image large enough so that all the glyphs
are actually rendered and not skipped which would not overflow the
cache.
This test is specifically engineered to trigger an overflow in the glyph
renderer that was theorized on IRC with an earlier patchset.
If only one slice was available, and that slice was not high enough to
hold the glyph we were trying to put in there, it would allocate a slice
that was too small. The check for the size was missing.
So now add a test that fills up all the slices in the glyph cache apart
from one and than tries to add one final glyph that is too large for the
last slice.
