vclwidget: add some safety net asserts

Change-Id: I5fa19ec6161ab97eb7df8b52a268917f41ae2205

include/vcl/outdev.hxx

@@ -274,11 +274,13 @@ private:
 
     inline void acquire() const
     {
+        assert(!mbDisposed);
         mnRefCnt++;
     }
 
     inline void release() const
     {
+        assert(mnRefCnt>0);
         if (!--mnRefCnt)
             delete const_cast<OutputDevice*>(this);
     }

include/vcl/vclptr.hxx

@@ -270,6 +270,7 @@ public:
     ~ScopedVclPtr()
     {
         VclPtr<reference_type>::disposeAndClear();
+        assert(VclPtr<reference_type>::get() == nullptr); // make sure there are no lingering references
     }
 private:
     // Most likely we don't want this default copy-construtor.