Fix potential bug in loop normals code.

Even if we cannot use computed lnor, we still have to empty the fan stack of lnors!

source/blender/blenkernel/intern/mesh_evaluate.c

@@ -567,6 +567,10 @@ void BKE_mesh_normals_loop_split(MVert *mverts, const int UNUSED(numVerts), MEdg
 						copy_v3_v3(nor, lnor);
 					}
 				}
+				else {
+					/* We still have to clear the stack! */
+					while (BLI_SMALLSTACK_POP(normal));
+				}
 			}
 
 			ml_prev = ml_curr;

source/blender/bmesh/intern/bmesh_mesh.c

@@ -641,6 +641,10 @@ static void bm_mesh_loops_calc_normals(BMesh *bm, const float (*vcos)[3], const
 						copy_v3_v3(nor, lnor);
 					}
 				}
+				else {
+					/* We still have to clear the stack! */
+					while (BLI_SMALLSTACK_POP(normal));
+				}
 			}
 		} while ((l_curr = l_curr->next) != l_first);
 	}