Test the panic cases for gocrunch/mat

[NDari]

With the usage of panic in the cases of errors, it is now possible to implement testing for these errors using recover. this should be implemented for all panicing cases in gocrunch/mat, and should be demanded of all future modules.

Acceptance Criteria:

• The errors in the mat library have been converted into a global slice of strings (similar to the errStrings slice in gocrunch/vec).
• All panic cases in the mat library are tested, and the correct error message is thrown.