Update segment tree walk logic with good flag

Refactor segment tree walk function to use a boolean flag for condition checking.

Author: lrvideckis

library/data_structures_[l,r]/seg_tree_uncommon/walk.hpp

@@ -13,10 +13,12 @@ int walk(int l, int r, const auto& f) {
       return u - n;
     }
   */
+  bool good=0;
   while (l <= r) {
-    int u = l + n, x = __lg(min(u & -u, r - l));
-    if (f(s[u >> x])) r = l + (1 << x) - 1;
+    int u = l + n, x = __lg(min(u & -u, r - l + 1));
+    if (f(s[u >> x])) good=1,r = l + (1 << x) - 1;
     else l += 1 << x;
   }
-  return -1;
+  return good ? l ; -1;
+ // return l;
 }