Clear the error list before second LaTeX run

Clear the error list before second LaTeX run

It was possible for errors that occured in the first run to be shown
in the error list after the second run. Now, the errors are cleared
before the second run.

Although I do not have a reproducible example at hand, I imagine
this situation would occur if a rerun is required and there is still
an error after the rerun.

Related to #9765.