Method decrease

lib/mu-labels-cache.hh:81–89

* Remove a label occurrence from the cache * * Removes the label completely if this was the _last_ occurence. * * @param label some label */

	 * @param label some label
	 */
	void decrease(const std::string& label) {
		if (auto it = label_map_.find(label); it != label_map_.end()) {
			if (it->second == 1)
				label_map_.erase(it);
			else
				--it->second;
			++dirty_;
		}
	}

	/**
	 * Update the cache with the label changes