getDiffRanges: better fallback for absent patch #3572

Job	Run time
Diagnostic export (ubuntu-latest, nightly-latest)	54s
Diagnostic export (ubuntu-latest, linked)	53s
Diagnostic export (windows-latest, linked)	3m 18s
Diagnostic export (macos-latest, linked)	1m 10s
Diagnostic export (windows-latest, nightly-latest)	3m 55s
Diagnostic export (macos-latest, nightly-latest)	1m 19s
	11m 29s

Provide feedback