Fix yellow/red coloring while rebasing

It determines the yellow/red status by getting the merge-base between the
current branch and its upstream; while we're rebasing, the current branch is
HEAD, so it tried to get the merge-base between HEAD and HEAD{u}, which doesn't
work. Fix this by passing the name of the checked-out branch separately.

pkg/gui/controllers/switch_to_sub_commits_controller.go

@@ -64,6 +64,7 @@ func (self *SwitchToSubCommitsController) viewCommits() error {
 			FilterPath:           self.c.Modes().Filtering.GetPath(),
 			IncludeRebaseCommits: false,
 			RefName:              ref.FullRefName(),
+			RefForPushedStatus:   ref.FullRefName(),
 		},
 	)
 	if err != nil {