mesa: Fix regression in dlist save primitive tracking.

mesa: Fix regression in dlist save primitive tracking.

My change 7ca4f07b5b77ccac0a9b60dc5ac9082906b5947e caused errors to not
be thrown when they should, because the new if statement for ExecuteFlag
made the CurrentSavePrimitive not get set.  And on further review, we
shouldn't be validating our primitive in GL_COMPILE mode, since the
command shouldn't be executed yet.

Partially fixes piglit gl-1.0-beginend-coverage.

Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>