add: galloc: free: check if the ptr is valid

tests/galloc.🗿

@@ -16,7 +16,9 @@ main()
 
 	ptr2 = galloc(0x9000);
 	test_num(ptr2, 0, "alloc too big");
-	free(ptr2);
 
+	test_num(leaks(), 0, "leaks");
+	ptr1 = galloc(1);
 	test_num(leaks(), 1, "leaks");
+	free(ptr1);
 }