Fix part 1 of bug #9771 with assertion violation in move_it_by_lines.

 src/xdisp.c (move_it_vertically_backward): Don't look for character position
 immediately after the newline when in a continuation line.

src/ChangeLog

@@ -3,6 +3,9 @@
 	* xdisp.c (push_display_prop): Determine whether to record string
 	or buffer position by IT->string, not by IT->method.  Allow
 	GET_FROM_DISPLAY_VECTOR as IT->method on entry.  (Bug#9771, part 4)
+	(move_it_vertically_backward): Don't look for character position
+	immediately after the newline when in a continuation line.
+	(Bug#9771, part 1)
 
 2011-10-15  Martin Rudalics  <rudalics@gmx.at>
 

src/xdisp.c

@@ -8768,7 +8768,10 @@ move_it_vertically_backward (struct it *it, int dy)
 	 reordering.  We want to get to the character position
 	 that is immediately after the newline of the previous
 	 line.  */
-      if (it->bidi_p && IT_CHARPOS (*it) > BEGV
+      if (it->bidi_p
+	  && !it->continuation_lines_width
+	  && !STRINGP (it->string)
+	  && IT_CHARPOS (*it) > BEGV
 	  && FETCH_BYTE (IT_BYTEPOS (*it) - 1) != '\n')
 	{
 	  EMACS_INT nl_pos =