Fixed crash issue by remove

ERROR:../../libgee-0.20.6/gee/arraylist.c:736:gee_array_list_real_get: assertion failed: (index < _size)
Bail out! ERROR:../../libgee-0.20.6/gee/arraylist.c:736:gee_array_list_real_get: assertion failed: (index < _size)

The follow code will throw the error:

	var file_list = new Gee.ArrayList<File>();
	file_list.add(File.new_for_path ("One"));
	file_list.add(File.new_for_path ("Two"));
	file_list.add(File.new_for_path ("Three"));
	file_list.add(File.new_for_path ("Four"));
	file_list.add(File.new_for_path ("Five"));
	foreach(var file in file_list) {
		GLib.warning("File is %s", file.get_path ());
		file_list.remove (file);
	}