Preserve commit message when quitting while the commit message panel is open

This isn't possible with the default quit binding ('q'), but there's an
alternative binding (ctrl-c) that does work while the panel is open; also, users
can rebind quit to something like ctrl-q.

pkg/gui/controllers/commit_description_controller.go

@@ -91,6 +91,12 @@ func (self *CommitDescriptionController) GetOnFocus() func(types.OnFocusOpts) {
 	}
 }
 
+func (self *CommitDescriptionController) GetOnQuit() func() {
+	return func() {
+		self.c.Helpers().Commits.PreserveCommitMessage()
+	}
+}
+
 func (self *CommitDescriptionController) switchToCommitMessage() error {
 	self.c.Context().Replace(self.c.Contexts().CommitMessage)
 	return nil

pkg/gui/controllers/commit_message_controller.go

@@ -82,6 +82,12 @@ func (self *CommitMessageController) GetOnFocusLost() func(types.OnFocusLostOpts
 	}
 }
 
+func (self *CommitMessageController) GetOnQuit() func() {
+	return func() {
+		self.c.Helpers().Commits.PreserveCommitMessage()
+	}
+}
+
 func (self *CommitMessageController) Context() types.Context {
 	return self.context()
 }