fix(polygon): clear next_url between free and re-assign in pagination

src/providers/polygon.zig

@@ -102,7 +102,14 @@ pub const Polygon = struct {
             var response = try self.client.get(authed);
             defer response.deinit();
 
+            // Free the cursor URL we just consumed and clear next_url
+            // BEFORE attempting to parse. If parseDividendsPage errors,
+            // the function-scope defer at the top must not see a
+            // dangling pointer in next_url -- otherwise it double-frees
+            // the buffer we just released. The new next_url (if any)
+            // gets assigned below on success.
             allocator.free(cursor_url);
+            next_url = null;
             next_url = try parseDividendsPage(allocator, response.body, &all_dividends);
         }