🐛 Fix applying an amended commit

When applying an amended commit, the validation routine considered no
changes in the tree as invalid. This condition occurs when only
changing the message and no files.

internal/ui/ui.go

@@ -451,7 +451,7 @@ func (m Model) commit(q quit) Model {
 }
 
 func (m Model) validate() bool {
-	return m.state.Repository.Worktree.IsStaged() && m.models.header.Summary() != ""
+	return (m.state.Repository.Worktree.IsStaged() || m.amend) && m.models.header.Summary() != ""
 }
 
 func (m *Model) restoreModel(save savedState) {