Fix a crash that's easily triggered by our malloc().

https://github.com/mbert/elvis/commit/5c3c8ec827fe

--- draw.c.orig	Tue Oct 21 04:32:25 2003
+++ draw.c	Tue Aug 16 19:59:52 2016
@@ -1114,7 +1114,7 @@ static void updateimage(win)
 			logicaltab = 0;
 		else
 		{
-			for (i = 0; di->newline[i].startrow < row && di->newline[i + 1].startrow - 1 < row; i++)
+			for (i = 0; di->newline[i].startrow < row && di->nlines > i && di->newline[i + 1].startrow - 1 < row; i++)
 			{
 			}
 			logicaltab = (row - di->newline[i].startrow) * ncols;