Fix T98520: Sculpt operators can unintentionally clear multires mask

Typo in {rBcf69652618fe}.

Maniphest Tasks: T98520

Differential Revision: https://developer.blender.org/D15087

source/blender/blenkernel/intern/subdiv_ccg_mask.c

@@ -155,7 +155,7 @@ static void mask_init_functions(SubdivCCGMaskEvaluator *mask_evaluator)
 bool BKE_subdiv_ccg_mask_init_from_paint(SubdivCCGMaskEvaluator *mask_evaluator,
                                          const struct Mesh *mesh)
 {
-  if (CustomData_get_layer(&mesh->ldata, CD_GRID_PAINT_MASK)) {
+  if (!CustomData_get_layer(&mesh->ldata, CD_GRID_PAINT_MASK)) {
     return false;
   }
   /* Allocate all required memory. */