fixup! Add command "Rebase onto base branch" to rebase menu

Author: stefanhaller

pkg/gui/controllers/helpers/merge_and_rebase_helper.go

@@ -241,7 +241,7 @@ func (self *MergeAndRebaseHelper) RebaseOntoRef(ref string) error {
 		disabledReason = &types.DisabledReason{Text: self.c.Tr.CantRebaseOntoSelf}
 	}
 
-	baseBranch, err := self.c.Git().Loaders.BranchLoader.GetBaseBranch(checkedOutBranch, self.refsHelper.c.Model().ExistingMainBranches)
+	baseBranch, err := self.c.Git().Loaders.BranchLoader.GetBaseBranch(checkedOutBranch, self.refsHelper.c.Model().MainBranches)
 	if err != nil {
 		return err
 	}