In DPTA only, draping onto reality data does not work when the model-being-draped is disabled

[markschlosseratbentley]

This can be reproduced using branch drape-onto-reality referenced in this PR: #7637

1. Use DPTA in itwinjs-core/tests-apps/display-performance-test-app to run a single test with a saved view where:
   a. reality data draping is enabled (see above PR for how to enable this)
   b. the model from the iModel which is being draped is disabled
2. Observe that the draping does not show up.
3. Recall the same saved view in DTA in itwinjs-core/test-apps/display-test-app.
4. Observe that the draping does show up.

Note that other draping views work properly in DPTA. The problem only occurs when the model-being-draped is disabled.

[markschlosseratbentley]

It appears the problem may only be limited to glTF reality datasets. b3dm appears to work properly with the same scenario.

fyi @danielzhong-bentley

[danielzhong-bentley]

This is resolved