kconfig: make use of menu_get_ext_help in gconfig

Futhermore, gconfig interface lack the "search a symbol" function, do later.

Signed-off-by: Cheng Renquan <crquan@gmail.com>
Cc: Roman Zippel <zippel@linux-m68k.org>
[sam: fix SEGV in gconfig]
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
diff --git a/scripts/kconfig/menu.c b/scripts/kconfig/menu.c
index 931d782..b74f746 100644
--- a/scripts/kconfig/menu.c
+++ b/scripts/kconfig/menu.c
@@ -528,5 +528,6 @@
 	} else {
 		str_append(help, nohelp_text);
 	}
-	get_symbol_str(help, sym);
+	if (sym)
+		get_symbol_str(help, sym);
 }