Fix T100673: crash when using slide brush without attachment info

The slide brush requires attachment information on the curves.
Now a warning is shown instead of crashing Blender. The attachment
information can be generated by executing the
`Curves > Snap to Nearest Surface` operator.

source/blender/editors/sculpt_paint/curves_sculpt_slide.cc

@@ -149,6 +149,12 @@ struct SlideOperationExecutor {
       report_missing_uv_map_on_original_surface(stroke_extension.reports);
       return;
     }
+    if (curves_orig_->surface_uv_coords().is_empty()) {
+      BKE_report(stroke_extension.reports,
+                 RPT_WARNING,
+                 TIP_("Curves do not have surface attachment information"));
+      return;
+    }
     const StringRefNull uv_map_name = curves_id_orig_->surface_uv_map;
 
     curves_sculpt_ = ctx_.scene->toolsettings->curves_sculpt;