master aff5961274: Avoid assertion violations in 'back_to_previous_visible_line_start'

[Eli Zaretskii]

branch: master
commit aff596127476c0fbcb11ccbbce63f32d03785653
Author: Eli Zaretskii <eliz@gnu.org>
Commit: Eli Zaretskii <eliz@gnu.org>

    Avoid assertion violations in 'back_to_previous_visible_line_start'
    
    * src/xdisp.c (init_iterator): Always initialize narrowed_begv to
    zero, since SET_WITH_NARROWED_BEGV depends on it being non-zero as
    an indication that long-line optimizations are in use.
    (back_to_previous_visible_line_start): When long-line
    optimizations are in effect, we may end up not on a newline.
---
 src/xdisp.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/src/xdisp.c b/src/xdisp.c
index 099efed2db..3ca0022a6d 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -3473,8 +3473,9 @@ init_iterator (struct it *it, struct window *w,
                        &it->bidi_it);
        }
 
-      if (current_buffer->long_line_optimizations_p)
-       it->narrowed_begv = 0;
+      /* This is set only when long_line_optimizations_p is non-zero
+        for the current buffer.  */
+      it->narrowed_begv = 0;
 
       /* Compute faces etc.  */
       reseat (it, it->current.pos, true);
@@ -7412,7 +7413,7 @@ back_to_previous_visible_line_start (struct it *it)
   it->continuation_lines_width = 0;
 
   eassert (IT_CHARPOS (*it) >= BEGV);
-  eassert (it->narrowed_begv > BEGV
+  eassert (it->narrowed_begv > 0 /* long-line optimizations: all bets off */
           || IT_CHARPOS (*it) == BEGV
           || FETCH_BYTE (IT_BYTEPOS (*it) - 1) == '\n');
   CHECK_IT (it);