core: Fix new proxy credentials being ignored

Changing proxy authentication credentials had no effect because of
the internal QNetworkAccessManager cache.

src/libs/core/application.cpp

@@ -208,7 +208,11 @@ void Application::applySettings()
             proxy.setUser(m_settings->proxyUserName);
             proxy.setPassword(m_settings->proxyPassword);
         }
+
         QNetworkProxy::setApplicationProxy(proxy);
+
+        // Force NM to pick up changes.
+        m_networkManager->clearAccessCache();
         break;
     }
     }