Fix adding blank line at end of commit message

[stefanhaller]

• PR Description

This fixes a bug where adding enough new lines to a commit message description such that it becomes taller than the window so that the window needs to resize vertically, the cursor wouldn't move to the added blank line, but stay at the end of the previous line. This was a regression introduced with #4152.

• Please check if the PR fulfills these requirements

• Cheatsheets are up-to-date (run go generate ./...)
• Code has been formatted (see here)
• Tests have been added/updated (see here for the integration test guide)
• Text is internationalised (see here)
• If a new UserConfig entry was added, make sure it can be hot-reloaded (see here)
• Docs have been updated if necessary
• You've read through your own file changes for silly mistakes etc

[codacy-production]

Coverage summary from Codacy

See diff coverage on Codacy

Coverage variation	Diff coverage
Report missing for a77dcbe1	✅ 92.31%

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (a77dcbe)	Report Missing	Report Missing	Report Missing
Head commit (20d0b43)	52030	44980	86.45%

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 (#4182)	13	12	92.31%

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

1. Codacy didn't receive coverage data for the commit, or there was an error processing the received data. Check your integration for errors and validate that your coverage setup is correct. ↩

[jesseduffield]

LGTM