Diff-informed analysis: fix empty PR handling #285

Job	Run time
Upload debug artifacts after failure in analyze (default)	1m 35s
Upload debug artifacts after failure in analyze (stable-v2.20.3)	1m 52s
Upload debug artifacts after failure in analyze (nightly-latest)	1m 37s
Upload debug artifacts after failure in analyze (linked)	1m 26s
Download and check debug artifacts after failure in analyze	4s
	6m 34s

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