unlock mutex around lok_preload_hook

because it now instantiates some services

Change-Id: Ia4f7c2df9f8dca3334906f0b482853002666ddd8
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/164484
Tested-by: Jenkins
Reviewed-by: Miklos Vajna <vmiklos@collabora.com>

cppuhelper/source/servicemanager.cxx

@@ -1981,7 +1981,10 @@ void cppuhelper::ServiceManager::preloadImplementations() {
             if (std::find(aPreloaded.begin(), aPreloaded.end(), fpPreload) == aPreloaded.end())
             {
                 aPreloaded.push_back(fpPreload);
+                // unlock because we may be instantiating some services here
+                g.unlock();
                 fpPreload();
+                g.lock();
             }
         }