*While I cannot guarantee that this will fix the recent intermittents, this patch really shouldn't hurt.*
By setting the Image `src` first, there's a small possibility that the Image is loaded *before* we've had a change to attach the `onload`/`onerror` callbacks which may cause the Promise to remain in a pending state.
Note that prior to PR 13641 we didn't correctly await all image resources to actually load, which could explain the very recent intermittent test-failures.
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