[fido] Fix wrong dialog shown when setting PIN

Fix a bug where trying to set a new PIN on a security key shows the
update PIN dialog instead. Attempting to use that dialog results in a
CHECK, since a PIN that is not set in the first place can't be changed.

Fixed: 1152548
Change-Id: I375b4b550009726fe3ec865400443871cda1ea2f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2558916
Auto-Submit: Nina Satragno <nsatragno@chromium.org>
Reviewed-by: dpapad <dpapad@chromium.org>
Commit-Queue: dpapad <dpapad@chromium.org>
Commit-Queue: Nina Satragno <nsatragno@chromium.org>
Cr-Commit-Position: refs/heads/master@{#830710}

chrome/browser/ui/webui/settings/settings_security_key_handler.cc

@@ -125,6 +125,7 @@ void SecurityKeysPINHandler::OnGatherPIN(uint32_t current_min_pin_length,
     response.emplace("retries", static_cast<int>(*num_retries));
   } else {
     state_ = State::kGatherNewPIN;
+    response.emplace("retries", base::Value::Type::NONE);
   }
 
   ResolveJavascriptCallback(base::Value(std::move(callback_id_)),