fix: fixed a bug in XORBasis.insert()

Author: a1fredbao

src/alfred/math/linear.hpp

@@ -146,6 +146,7 @@ struct XORBasis {
                 return i;
             } else x ^= p[i];
         }
+        has_zero = true;
         return -1;
     }
     inline T max(T ans = 0) {