Fix rare crash in interactive rebase (merge command without comment) (#4872)

This fixes a crash in an interactive rebase when there's a merge command
in the rebase-todo file that doesn't have a comment. I don't know under
what circumstances this can happen; git itself doesn't produce these,
but it is theoretically possible for the user to do this manually by
doing `git rebase --edit-todo`, or third-party tools could do it too.

We had one user report a crash because of this, so it seems worth fixing
it.

Closes #4858.

Author: stefanhaller

go.mod

@@ -32,7 +32,7 @@ require (
 	github.com/sirupsen/logrus v1.9.3
 	github.com/spf13/afero v1.9.5
 	github.com/spkg/bom v0.0.0-20160624110644-59b7046e48ad
-	github.com/stefanhaller/git-todo-parser v0.0.7-0.20250429125209-dcf39e4641f5
+	github.com/stefanhaller/git-todo-parser v0.0.7-0.20250905083220-c50528f08304
 	github.com/stretchr/testify v1.10.0
 	github.com/xo/terminfo v0.0.0-20210125001918-ca9a967f8778
 	golang.org/x/exp v0.0.0-20240719175910-8a7402abbf56

go.sum

@@ -284,8 +284,8 @@ github.com/spf13/afero v1.9.5 h1:stMpOSZFs//0Lv29HduCmli3GUfpFoF3Y1Q/aXj/wVM=
 github.com/spf13/afero v1.9.5/go.mod h1:UBogFpq8E9Hx+xc5CNTTEpTnuHVmXDwZcZcE1eb/UhQ=
 github.com/spkg/bom v0.0.0-20160624110644-59b7046e48ad h1:fiWzISvDn0Csy5H0iwgAuJGQTUpVfEMJJd4nRFXogbc=
 github.com/spkg/bom v0.0.0-20160624110644-59b7046e48ad/go.mod h1:qLr4V1qq6nMqFKkMo8ZTx3f+BZEkzsRUY10Xsm2mwU0=
-github.com/stefanhaller/git-todo-parser v0.0.7-0.20250429125209-dcf39e4641f5 h1:ZCI0NPs0xXd00Ej9lX+wwbHjQDkstJa3kUbX7WCOF8I=
-github.com/stefanhaller/git-todo-parser v0.0.7-0.20250429125209-dcf39e4641f5/go.mod h1:HFt9hGqMzgQ+gVxMKcvTvGaFz4Y0yYycqqAp2V3wcJY=
+github.com/stefanhaller/git-todo-parser v0.0.7-0.20250905083220-c50528f08304 h1:bg+K3E0GYuqwTGaEfNrsZ0rH0Bw4p3EmPjk9Zjnua+w=
+github.com/stefanhaller/git-todo-parser v0.0.7-0.20250905083220-c50528f08304/go.mod h1:HFt9hGqMzgQ+gVxMKcvTvGaFz4Y0yYycqqAp2V3wcJY=
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
 github.com/stretchr/testify v0.0.0-20161117074351-18a02ba4a312/go.mod h1:a8OnRcib4nhh0OaRAV+Yts87kKdq0PP7pXfy6kDkUVs=
 github.com/stretchr/testify v1.2.2/go.mod h1:a8OnRcib4nhh0OaRAV+Yts87kKdq0PP7pXfy6kDkUVs=

vendor/github.com/stefanhaller/git-todo-parser/todo/parse.go

@@ -321,7 +321,7 @@ github.com/spf13/afero/mem
 # github.com/spkg/bom v0.0.0-20160624110644-59b7046e48ad
 ## explicit
 github.com/spkg/bom
-# github.com/stefanhaller/git-todo-parser v0.0.7-0.20250429125209-dcf39e4641f5
+# github.com/stefanhaller/git-todo-parser v0.0.7-0.20250905083220-c50528f08304
 ## explicit; go 1.13
 github.com/stefanhaller/git-todo-parser/todo
 # github.com/stretchr/testify v1.10.0