Patch Segfault Error for Experimental Matlab Toolbox

[ssun30]

Changes proposed in this pull request

• Added extra error handling for mole fraction and mass fraction setters in the new matlab toolbox.

If applicable, fill in the issue number this pull request is fixing

• Setting X and Y with an empty array/string OR arrays of incorrect length (not matching the number of species) will cause a segfault error and instantly crashes Matlab.
• This patch is necessary for the Matlab test suite (Matlab interface (new) test suite #1496) to run without crashing.

Checklist

• The pull request includes a clear description of this code change
• Commit messages have short titles and reference relevant issues
• Build passes (scons build & scons test) and unit tests address code coverage
• Style & formatting of contributed code follows contributing guidelines
• The pull request is ready for review

[ischoegl]

Thanks - looks good to me!