Fix GAP_IsMatrix

... and make `GAP_IsMatrixOrMatrixObj`, `GAP_IsMatrixObj` future proof:
directly calling `DoFilter` is risky and will break as soon as the
"filter" we are passing in is not a true filter, but e.g. an and-filter
(such as `IsMatrix`)

src/libgap-api.c

@@ -420,19 +420,19 @@ static Obj NrColsAttr;
 // Returns 1 if <obj> is a GAP matrix or matrix obj, 0 if not.
 int GAP_IsMatrixOrMatrixObj(Obj obj)
 {
-    return obj && DoFilter(IsMatrixOrMatrixObjFilt, obj) == True;
+    return obj && CALL_1ARGS(IsMatrixOrMatrixObjFilt, obj) == True;
 }
 
 // Returns 1 if <obj> is a GAP matrix, 0 if not.
 int GAP_IsMatrix(Obj obj)
 {
-    return obj && DoFilter(IsMatrixFilt, obj) == True;
+    return obj && CALL_1ARGS(IsMatrixFilt, obj) == True;
 }
 
 // Returns 1 if <obj> is a GAP matrix obj, 0 if not.
 int GAP_IsMatrixObj(Obj obj)
 {
-    return obj && DoFilter(IsMatrixObjFilt, obj) == True;
+    return obj && CALL_1ARGS(IsMatrixObjFilt, obj) == True;
 }
 
 // Returns the number of rows of the given GAP matrix obj.