GPv3: Fix initial selection mask of the grab sculpt tool

The initial mouse sample has a pressure of zero, which excludes all
points from the selection when the grab tool starts. Use a pressure of
1 to ensure all points are included.

Pull Request: https://projects.blender.org/blender/blender/pulls/121183

source/blender/editors/sculpt_paint/grease_pencil_sculpt_grab.cc

@@ -159,12 +159,13 @@ void GrabOperation::on_stroke_begin(const bContext &C, const InputSample &start_
 
     Array<float2> view_positions = calculate_view_positions(params, selection);
 
+
     /* Cache points under brush influence. */
     Vector<float> weights;
     IndexMask point_mask = brush_influence_mask(scene,
                                                 brush,
                                                 start_sample.mouse_position,
-                                                start_sample.pressure,
+                                                1.0f,
                                                 info.multi_frame_falloff,
                                                 selection,
                                                 view_positions,