Fix bug #11587 with a crash in an Info buffer under linum-mode.

 src/xdisp.c (handle_stop): Detect whether we have overlay strings
 loaded by testing it->current.overlay_string_index to be
 non-negative, instead of checking whether n_overlay_strings is
 positive.

src/ChangeLog

+2012-05-30  Eli Zaretskii  <eliz@gnu.org>
+
+	* xdisp.c (handle_stop): Detect whether we have overlay strings
+	loaded by testing it->current.overlay_string_index to be
+	non-negative, instead of checking whether n_overlay_strings is
+	positive.  (Bug#11587)
+
 2012-05-30  Chong Yidong  <cyd@gnu.org>
 
 	* keymap.c (describe_map_tree): Revert 2011-07-07 change (Bug#1169).

src/xdisp.c

@@ -3157,7 +3157,7 @@ handle_stop (struct it *it)
 		     onto the stack one more time, which is not
 		     expected by the rest of the code that processes
 		     overlay strings.  */
-		  || (it->n_overlay_strings <= 0
+		  || (it->current.overlay_string_index < 0
 		      ? !get_overlay_strings_1 (it, 0, 0)
 		      : 0))
 		{