Fix moving a custom patch from the very first commit of the history to a later commit (#4631)

- **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.

pkg/commands/git_commands/patch.go

@@ -162,7 +162,7 @@ func (self *PatchCommands) MovePatchToSelectedCommit(commits []*models.Commit, s
 	self.os.LogCommand(logTodoChanges(changes), false)
 
 	err := self.rebase.PrepareInteractiveRebaseCommand(PrepareInteractiveRebaseCommandOpts{
-		baseHashOrRoot: commits[baseIndex].Hash(),
+		baseHashOrRoot: getBaseHashOrRoot(commits, baseIndex),
 		overrideEditor: true,
 		instruction:    daemon.NewChangeTodoActionsInstruction(changes),
 	}).Run()