Fix moving a custom patch from the very first commit of the history to a later commit

[stefanhaller]

• PR Description

Moving a custom patch from the very first commit of the history to a later commit would crash with an index-out-of-range error.

I double-checked that all other callers of PrepareInteractiveRebaseCommand already call getBaseHashOrRoot, so this was the only one that was broken.

I decided not to add a test for this as the scenario is not a very common one.

Fixes #4624.

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[codacy-production]

Coverage summary from Codacy

See diff coverage on Codacy

Coverage variation	Diff coverage
Report missing for aa331e51	✅ 100.00%

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (aa331e5)	Report Missing	Report Missing	Report Missing
Head commit (9aaec5e)	56637	49194	86.86%

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#4631)	1	1	100.00%

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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Footnotes

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