using a mouse and "continuous zoom modus" enabled, the vzd->timer_lastdraw gets updated until the modal exits but with a trackpad it never enters the modal state and vzd->timer_lastdraw is not not set.

Moving vzd->timer_lastdraw = PIL_check_seconds_timer(); earier in the invoke or adding a timer does not help because for each movement on the trackpad the function gets immediately applied (view_zoomdrag_invoke -> view_zoomdrag_init -> view_zoomdrag_apply).

I thought of A) adding a fake vzd->timer_lastdraw = PIL_check_seconds_timer() - 10; to the corresponding if branch in view_zoomdrag_invoke to satisfy view_zoomdrag_apply or B) add a time_step = MIN2(time_step, 10); to the to this hunk in view_zoomdrag_apply.

/* continuous zoom shouldn't move that fast... */
 if (U.viewzoom == USER_ZOOM_CONT) {  // XXX store this setting as RNA prop?
   double time = PIL_check_seconds_timer();
   float time_step = (float)(time - vzd->timer_lastdraw);

   time_step = MIN2(time_step, 10);

   dx *= time_step * 0.5f;
   dy *= time_step * 0.5f;

   vzd->timer_lastdraw = time;
 }

Both feel hackish, maybe someone has a better idea.

view3d_edit.c, image_ops.c and clip_ops.c all have code for continuous zoom as well. If they don't suffer from the same issue, then you could copy the logic from those?

@Brecht Van Lommel (brecht) ping

I applied the patch against current blender-v2.82-release, and pinch zooming with Continue zoom + Zoom to Mouse no longer crashes in i.e. node editor.

I am under the impression that this code can be deduplicated.
Part of the logic is seen in view_zoomdrag_apply

This patch breaks zooming in other editors such as Graph Editors,
which have the ability to independently scale by x/y.