Add residual to solver (fix regression from 087cd1c)

qpms/beyn.c

@@ -485,10 +485,10 @@ static int beyn_process_matrices(BeynSolver *solver, beyn_function_M_t M_functio
     if (res_tol > 0 && residual > res_tol) continue;
 
     eigenvalues[KRetained] = z;
-    if(eigenvectors) {
+    if(eigenvectors) { // eigenvectors is NULL when calculating the "coarse" contour for error estimates
       for(int j = 0; j < m; ++j) 
         MAT(eigenvectors, l, m, KRetained, j) = MAT(V0S, m, K, j, k);
-
+      solver->residuals[KRetained] = residual;
     }
     ++KRetained;
   }