patch 9.0.2134: ml_get error when scrolling

Problem:  ml_get error when scrolling after delete
Solution: mark topline to be validated in main_loop
          if it is larger than current buffers line
          count

reset_lnums() is called after e.g. TextChanged autocommands and it may
accidentally cause curwin->w_topline to become invalid, e.g. if the
autocommand has deleted some lines.

So verify that curwin->w_topline points to a valid line and if not, mark
the window to have w_topline recalculated in main_loop() in
update_topline() after reset_lnums() returns.

fixes: #13568
fixes: #13578

Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/window.c b/src/window.c
index 55ce31c..0f4363b 100644
--- a/src/window.c
+++ b/src/window.c
@@ -7441,12 +7441,16 @@
 	{
 	    // Restore the value if the autocommand didn't change it and it was
 	    // set.
+	    // Note: This triggers e.g. on BufReadPre, when the buffer is not yet
+	    //       loaded, so cannot validate the buffer line
 	    if (EQUAL_POS(wp->w_save_cursor.w_cursor_corr, wp->w_cursor)
 				  && wp->w_save_cursor.w_cursor_save.lnum != 0)
 		wp->w_cursor = wp->w_save_cursor.w_cursor_save;
 	    if (wp->w_save_cursor.w_topline_corr == wp->w_topline
-				      && wp->w_save_cursor.w_topline_save != 0)
+				  && wp->w_save_cursor.w_topline_save != 0)
 		wp->w_topline = wp->w_save_cursor.w_topline_save;
+	   if (wp->w_save_cursor.w_topline_save > wp->w_buffer->b_ml.ml_line_count)
+		wp->w_valid &= ~VALID_TOPLINE;
 	}
 }