Certain globs cause a TypeError

It seems that using a globbing pattern such as `**/**/*.js` will cause the following error when running karma-coverage:

`PhantomJS 1.9.8 (Mac OS X 0.0.0) ERROR
TypeError: 'undefined' is not an object (evaluating '__cov_hmKLkt0YIrHx8V6$TQ0_kg.s['2']')`

In the karma.conf preprocessor object, the glob that caused this error was set up like:
`'app/!(vendor)**/**/!(*.spec).js': ['coverage']`

Changing the second *\* to a specific directory "fixed" the error:
`'app/!(vendor)**/specific-dirname/!(*.spec).js': ['coverage']`

Reproduce the failure using the glob patterns shown in the issue's karma.conf preprocessor configuration, then inspect how karma-coverage handles those patterns before PhantomJS reports the TypeError. Done means the glob completes without the undefined coverage error and coverage is generated for the matching files.

Written by the indexing model from the issue text.