An HP-GL wedge of almost no radius drawn with an adaptive line type
(LT-1;EW0.000001,0,0;) leaves a lone moveto. Fitting the dashes to its
corners indexed the empty segment list and panicked while rendering. Such
a subpath now uses the exact plan, which has no runs to fit.
Found by import_fuzz::random_hpgl_instructions_never_panic.