Auto merge of #7252 - nnethercote:fix-reporter-panics, r=Ms2ger
Auto merge of #7252 - nnethercote:fix-reporter-panics, r=Ms2ger

Fix panics in the script_task memory reporter.

These are caused by page_root being empty.

@jdm, I think it was #6874 that introduced these. I'm seeing them all the time when starting Servo on Reddit with memory profiling enabled. With this patch applied they go away.

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