Fix #299
Fix #299

When no input filename is given, the path is not actually
retained. This commit fixes this based on the suggested
edit of @jborch in #299.

PeterPablo/matlab2tikz,egeerardyn/matlab2tikz,LJeub/matlab2tikz,matlab2tikz/matlab2tikz,nidrosianDeath/matlab2tikz,okomarov/matlab2tikz,RPeschke/matlab2tikz,matlab2tikz/matlab2tikz,miscco/matlab2tikz,okomarov/matlab2tikz,egeerardyn/matlab2tikz