Fix #93289: Paint Mode stencil disappears when panning viewport

Code for drawing the cursor [this includes drawing the stencil] used to
early out when navigating.

This made it difficult to line up stencil projection with the 3D
geometry, so now still draw it while navigating.

Pull Request: https://projects.blender.org/blender/blender/pulls/131851

source/blender/editors/sculpt_paint/paint_cursor.cc

@@ -2154,6 +2154,8 @@ static void paint_draw_cursor(bContext *C, int x, int y, void * /*unused*/)
     return;
   }
   if (paint_cursor_is_3d_view_navigating(&pcontext)) {
+    /* Still draw stencil while navigating. */
+    paint_cursor_check_and_draw_alpha_overlays(&pcontext);
     return;
   }