Check all usage of |factory| in RegisterSchemeFactory().

The parameter |factory| of HttpAuthHandlerRegistryFactory::
RegisterSchemeFactory() maybe nullptr, move all usage of |factory|
in the check, make sure it will not crash.

Change-Id: Ic48b8e798bf26229436ccd2357a5c1a0dec789d7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2333912Reviewed-by: Zhongyi Shi <zhongyi@chromium.org>
Commit-Queue: Zhongyi Shi <zhongyi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#794893}

net/http/http_auth_handler_factory.cc

@@ -84,12 +84,13 @@ void HttpAuthHandlerRegistryFactory::SetHttpAuthPreferences(
 void HttpAuthHandlerRegistryFactory::RegisterSchemeFactory(
     const std::string& scheme,
     HttpAuthHandlerFactory* factory) {
-  factory->set_http_auth_preferences(http_auth_preferences());
   std::string lower_scheme = base::ToLowerASCII(scheme);
-  if (factory)
+  if (factory) {
+    factory->set_http_auth_preferences(http_auth_preferences());
     factory_map_[lower_scheme] = base::WrapUnique(factory);
-  else
+  } else {
     factory_map_.erase(lower_scheme);
+  }
 }
 
 HttpAuthHandlerFactory* HttpAuthHandlerRegistryFactory::GetSchemeFactory(