Fix T101370: GPencil Grab Sculpt crash after bake transform animation

The problem was the duplicated strokes had wrong pointers 
to the original stroke.

source/blender/editors/gpencil/gpencil_bake_animation.cc

@@ -298,6 +298,7 @@ static int gpencil_bake_grease_pencil_animation_exec(bContext *C, wmOperator *op
         BLI_addtail(&gpl_dst->frames, gpf_dst);
 
         LISTBASE_FOREACH (bGPDstroke *, gps, &gpf_dst->strokes) {
+          gps->runtime.gps_orig = NULL;
           /* Create material of the stroke. */
           Material *ma_src = BKE_object_material_get(elem->ob, gps->mat_nr + 1);
           bool found = false;
@@ -320,6 +321,8 @@ static int gpencil_bake_grease_pencil_animation_exec(bContext *C, wmOperator *op
           /* Update point location to new object space. */
           for (int j = 0; j < gps->totpoints; j++) {
             bGPDspoint *pt = &gps->points[j];
+            pt->runtime.idx_orig = 0;
+            pt->runtime.pt_orig = NULL;
             mul_m4_v3(ob_eval->obmat, &pt->x);
             mul_m4_v3(invmat, &pt->x);
           }