better handling for invalid `url` stanzas
chg `checklinks` to internal command `_checklinks`

* `checklinks` is a very simple implementation useful only for development purposes
* it has no test coverage, only one line of documentation
* users regularly experiment with it and break it, especially
 `brew cask checklinks` with no arguments, which tests all Tapped Casks
improve error message in `brew cask _dump`
update navicat-premium to version 11.1.5

* re-use version number
* update licence
re-use version + license in navicat-data-modeler
update navicat-for-mariadb to 11.1.5

* reuse version
* set license
update navicat-for-mysql to 11.1.5

* reuse version
* set license
update navicat-for-oracle to 11.1.5

* reuse version
* set license
update navicat-for-postgresql to 11.1.5

* reuse version
* set license
update navicat-for-sql-server to 11.1.5

* reuse version
* set license
update navicat-for-sqlite to 11.1.5

* reuse version
* set license
re-use version in bathyscaphe
re-use version in colorpicker-rcwebcolorpicker
re-use version in fourk-youtube-to-mp3
re-use version in graphsketcher
re-use version in pandora-one
re-use version in powerword
re-use version in razer-synapse
re-use version in trailer
re-use version in weka