domimplementation: Use rtl::Reference::get() instead of &*

Using &* can be problematic if the pointer is null. In this case it
doesn’t matter, but using Reference::get() is probably easier to
understand anyway. This also paves the way for a later compiler plugin
to check for this.

Change-Id: I9c055228f21639ad4005d71a768b335b40eff7e8
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/211843
Tested-by: Jenkins
Reviewed-by: Neil Roberts <nroberts@libreoffice.org>

unoxml/source/dom/domimplementation.cxx

@@ -33,7 +33,7 @@ namespace DOM
         // perhaps it would be helpful to know what the implementation should
         // do to answer this question...
         static rtl::Reference<CDOMImplementation> xDOMImplementation = new CDOMImplementation;
-        return &*xDOMImplementation;
+        return xDOMImplementation.get();
     }
 
     // there is just 1 static instance, so these must not delete it!