Fix PHP-1149 tests for invalid db/collection names

Restore max length check for DB names, which was removed when merging #756 for PHP-1265.
I believe this was inadvertently removed when `v1.5` was merged in: https://github.com/mongodb/mongo-php-driver/commit/afdf28268d0f47855a9f1e0f68d4e6f8dd075294#diff-61d70c33f4e01e6daaafe6855a3b76e9L52

The max length check logic was originally added in https://github.com/mongodb/mongo-php-driver/commit/908d7ee4c5b9f47df232a4e0fca91b1591fafc35 for #727 (PR for PHP-1149)