A more thorough fix for bug#19307

A more thorough fix for bug#19307

 src/xdisp.c (handle_stop, handle_single_display_spec)
 (next-element_from_image): Don't reset the
 ignore_overlay_strings_at_pos_p flag here.
 (next_element_from_buffer): Reset ignore_overlay_strings_at_pos_p
 here.
 (next_overlay_string): Set ignore_overlay_strings_at_pos_p here,
 after we've exhausted all the overlay strings at the current
 position.