renderer-native: Check that frame_info != NULL
A NULL value could be encountered when the monitor wakes from sleep as
pending_frame_infos might have been drained already during sleep via
dummy_power_save_page_flip.
If pending_frame_infos is empty then we don't care. It was only being
filled in as an optional courtesy. When not available (like during power
saving) just skip it, same as before commit e9e4b2b7.
First reported in #735 (closed)