fix(err): stackframes: skip empty list, get context per-event

[oliverb123]

Noticed we were making API requests:

• When toggling the in-app toggle if there was more than one exception in the exception list, and one of those exceptions was all in-app frames
• Even if there were no new frames to fetch, which happens in the above case (two exceptions in a single event, one with only in-app frames) if two events are "open", and you toggle the toggle on one of them (the logic's loadFrames was getting called, the filter in it filtered out all the frame id's because the other open event mean all the necessary contexts were loaded, but we'd still make the HTTP request with an empty list and get nothing back)

[github-actions[bot]]

Size Change: 0 B

Total Size: 1.16 MB

ℹ️ View Unchanged

| Filename | Size | | :--- | :---: | | `frontend/dist/toolbar.js` | 1.16 MB |

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