Add raw pointer check to IsUserVerifyingPlatformAuthenticatorAvailableImpl

Edge has been receiving reports of null pointer crashes similar to the
linked bug. We believe they are caused by
AuthenticatorCommon::IsUserVerifyingPlatformAuthenticatorAvailable
passing in a null delegate since
ContentBrowserClient::GetWebAuthenticationRequestDelegate
may return a nullptr if the embedder can't service the request.

To fix this we can check the pointer before calling the delegate

Bug: 1110081
Change-Id: I007a8815fb23e86e025e2ccafb2bcc74d40aebfc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2423049
Commit-Queue: Martin Kreichgauer <martinkr@google.com>
Reviewed-by: Martin Kreichgauer <martinkr@google.com>
Cr-Commit-Position: refs/heads/master@{#814152}

content/browser/webauth/authenticator_common.cc

@@ -497,6 +497,12 @@ bool IsUserVerifyingPlatformAuthenticatorAvailableImpl(
     AuthenticatorRequestClientDelegate* delegate,
     device::FidoDiscoveryFactory* discovery_factory,
     BrowserContext* browser_context) {
+  if (!delegate) {
+    // TODO(crbug/1110081): Investigate why this can be nullptr.
+    NOTREACHED();
+    return false;
+  }
+
   base::Optional<bool> is_uvpaa_override =
       delegate->IsUserVerifyingPlatformAuthenticatorAvailableOverride();
   if (is_uvpaa_override) {