fix: process of records without a ppn #113

Job	Run time
deny (bans licenses sources)	36s
fuzz (pica-record-ref, fuzz, fuzz-record-ref, 120)	3m 45s
deny (advisories)	31s
test (ubuntu-latest, stable, x86_64-unknown-linux-gnu)	1m 10s
fuzz (pica-record-matcher, fuzz, fuzz-record-matcher, 200)	4m 58s
test (ubuntu-latest, beta, x86_64-unknown-linux-gnu)	1m 19s
fuzz (pica-path, fuzz, fuzz-path, 200)	4m 56s
test (ubuntu-latest, nightly, x86_64-unknown-linux-gnu)	53s
fuzz (pica-format, fuzz, fuzz-format, 200)	5m 6s
test (windows-latest, stable, i686-pc-windows-msvc)	3m 29s
test (macos-latest, stable, x86_64-apple-darwin)	1m 15s
fuzz (pica-query, fuzz, fuzz-query, 200)	5m 4s
rustdoc	18s
outdated	4m 47s
clippy	22s
msrv	16s
rustfmt	14s
udeps	58s
publish	0s
ci	0s
	39m 57s

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