Fix `Gemfile.lock` parsing with zero dependencies (#1185) #3394

Job	Run time
deno-checks	14s
clippy (ubuntu-20.04)	5m 54s
clippy (self-hosted, macos, arm64)	49s
all-features (ubuntu-20.04)	9m 8s
all-features (self-hosted, macos, arm64)	1m 21s
oldstable (ubuntu-20.04)	5m 42s
oldstable (self-hosted, macos, arm64)	50s
rustfmt	16s
shellcheck	4s
test-matrix (ubuntu-20.04)	8m 32s
test-matrix (self-hosted, macos, arm64)	1m 15s
test	1s
	34m 6s

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