Fix bug #11417 with infloop when left-fringe/right-fringe spec is used on TTY.

Fix bug #11417 with infloop when left-fringe/right-fringe spec is used on TTY.

 src/xdisp.c (handle_stop): Don't call get_overlay_strings_1 if we
 already have overlays loaded.
 (handle_single_display_spec): Before returning without displaying
 fringe bitmap, synchronize the bidi iterator with the main display
 iterator, by calling iterate_out_of_display_property.
 (iterate_out_of_display_property): Detect buffer iteration by
 testing that it->string is a Lisp string.
 (get_next_display_element): When the current object is exhausted,
 and there's something on it->stack, call set_iterator_to_next to
 proceed with what's on the stack, instead of returning zero.
 (set_iterator_to_next): If called at the end of a Lisp string,
 proceed to consider_string_end without incrementing string
 position.  Don't increment display vector index past the end of
 the display vector.