segfault if 'tags' file is wrong format

[andy5995]

If the tags file is incorrectly formatted, bric will segfault when using the tagstack function.

To generate the correct tags file, the user must use Exuberant Ctags.

On Debian, the package exuberant-tags can be installed.

See this for more info. https://stackoverflow.com/questions/2968542/the-ctags-command-doesnt-recurse-saying-it-is-not-a-regular-file

Some debugging will needed to be done to find out what's specifically causing the segfault, and some type of check to see if the file is a proper tags file.