Black tiles are returned when rendering fails.
This happened due to bccu#1610 where internally
core collected cell info on the first 1024 rows
only. Anything beyond that always failed.
This limitation is now removed using dynamic
array to collect the cell info.
Regardless, the test here needs only check that
the last tile (really, anything beyond the 1024th row)
doesn't return a black tile.
This single tile still takes over 10 seconds to render,
which is the other issue that Core suffers from when
collecting cell info on a huge tab.
Change-Id: I7a1a5b7c2b2ed2cc4399160e096be5e57895af77
Reviewed-on: https://gerrit.libreoffice.org/25333
Reviewed-by: Ashod Nakashian <ashnakash@gmail.com>
Tested-by: Ashod Nakashian <ashnakash@gmail.com>
5d9140c3bb