fix: correct non null assert

Fix the typo in non null assertion. we
should check res_mat ofc.

Signed-off-by: Rodion Suvorov <rodion.suvorov.94@mail.ru>

Author: suvorovrain

experimental/algorithm/LAGraph_RPQMatrix.c

@@ -213,8 +213,8 @@ static GrB_Info LAGraph_RPQMatrixLor(RPQMatrixPlan *plan, char *msg)
     OK(LAGraph_RPQMatrix_solver(lhs, msg)) ;
     OK(LAGraph_RPQMatrix_solver(rhs, msg)) ;
 
-    LG_ASSERT(rhs->mat != NULL, GrB_NULL_POINTER) ;
-    LG_ASSERT(lhs->mat != NULL, GrB_NULL_POINTER) ;
+    LG_ASSERT(rhs->res_mat != NULL, GrB_NULL_POINTER) ;
+    LG_ASSERT(lhs->res_mat != NULL, GrB_NULL_POINTER) ;
 
     GrB_Matrix lhs_mat = lhs->res_mat ;
     GrB_Matrix rhs_mat = rhs->res_mat ;