[6/6] windowscodecs: Implement IPropertyBag2::Read

[Vincent Povirk]

+        if (idx > -1)
+        {
+            VariantInit(pvarValue+i);
+            res = VariantCopy(pvarValue+i, This->values+idx);
+            phrError[i] = res;
+            if (FAILED(res))
+                break;
+        }

This looks wrong to me. We have an array of error values to set for
each read attempt, so it seems like each read should be independent -
one failure shouldn't cause us to give up on the others, nor to free
the values we already read successfully.

If this is really how Windows works, we need a test for it.