Awesome: Avoid LaTeX error when label is undefined.

[ben-e-whitney]

According to the FRESH schema, the label property of the info object is not required. If a label is not provided, cv.tex will containe the command \position{}, which will define the macro \@position to be empty. When \makecvheader is expanded, we will get the following line.

\headerpositionstyle{\@position\\[\acvHeaderAfterPositionSkip]}

This will cause an error. We can sidestep the issue by only calling \position if a label (that will evaluate to true in the template) is given.

[hacksalot]

Very well. Thanks for the fix!