if tab clicked do imgui

for (unsigned i = 0; i < documents_.size(); i++) {

	auto* doc = &documents_[i];

	auto flag = doc->IsDirty() ? ImGuiTabItemFlags_UnsavedDocument : 0;
	if (pending_selection_uid_ == doc->uid_) {
		pending_selection_uid_ = 0;
		
		flag |= ImGuiTabItemFlags_SetSelected;
	}

	if (ImGui::BeginTabItem(doc->Title().c_str(), &doc->opened_, flag)){
		active_document_uid_ = doc->uid_;
		ImGui::EndTabItem();
	}
}