mask test: more thorough testing
mask test: more thorough testing

use a random mask to flip bits instead of flipping all bits. This will
help to find problems where only a subset of the mask entries is
compared.

Signed-off-by: Matthias Kretz <372ea4eca737a13cd010ee806d4ce7b98ee71550@kde.org>

chr-engwer/Vc,VcDevel/Vc,VcDevel/Vc,VcDevel/Vc,VcDevel/Vc,chr-engwer/Vc,chr-engwer/Vc