Fix more crashes attempting to run operators in unexpected contexts

Add missing NULL checks for:

- OBJECT_OT_transform_to_mouse
- GPENCIL_OT_time_segment_remove

source/blender/editors/object/object_add.cc

@@ -4031,7 +4031,7 @@ static int object_transform_to_mouse_exec(bContext *C, wmOperator *op)
 
     MEM_freeN(objects);
   }
-  else {
+  else if (CTX_wm_region_view3d(C)) {
     int mval[2];
     if (object_add_drop_xy_get(C, op, &mval)) {
       float cursor[3];

source/blender/editors/object/object_gpencil_modifier.c

@@ -1024,6 +1024,9 @@ static int time_segment_remove_exec(bContext *C, wmOperator *op)
   TimeGpencilModifierData *gpmd = (TimeGpencilModifierData *)gpencil_edit_modifier_property_get(
       op, ob, eGpencilModifierType_Time);
 
+  if (gpmd == NULL) {
+    return OPERATOR_CANCELLED;
+  }
   if (gpmd->segment_active_index < 0 || gpmd->segment_active_index >= gpmd->segments_len) {
     return OPERATOR_CANCELLED;
   }