Fix C-n/C-p when a line starts with an image

Fix C-n/C-p when a line starts with an image

* src/xdisp.c (move_it_to): Handle the case where the second call
to move_it_in_display_line_to under MOVE_TO_Y takes us farther
from TO_CHARPOS than the first call.  This fixes values returned
by pos-visible-in-window-p and posn-at-point when the screen line
starts with invisible text followed by an image.  (Bug#9092)