gnome-documents: hold solarmutex on dtor patch as well

Change-Id: I75fe71612116d435606c37185bf55b450425fc25
Reviewed-on: https://gerrit.libreoffice.org/37396Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>

include/comphelper/unique_disposing_ptr.hxx

@@ -171,6 +171,12 @@ public:
         SolarMutexGuard aGuard;
         unique_disposing_ptr<T>::reset(p);
     }
+
+    virtual ~unique_disposing_solar_mutex_reset_ptr() override
+    {
+        if (unique_disposing_ptr<T>::get() && comphelper::SolarMutex::get())
+            reset();
+    }
 };
 
 }