vis-lua: do not report errors recursively

Displaying an error might create a new window which in turn can
trigger new events (all other windows are resized+redrawn) which
might again cause errors.

There is still no sane way to exit the editor in this case, but
at least the error messages should be readable.

vis-core.h

@@ -164,6 +164,7 @@ struct Vis {
 	Buffer input_queue;                  /* holds pending input keys */
 	Buffer *keys;                        /* currently active keys buffer (either the input_queue or a macro) */
 	bool keyhandler;                     /* whether a key handling function is currently being called */
+	bool errorhandler;                   /* whether we are currently in an error handler, used to avoid recursion */
 	Action action;                       /* current action which is in progress */
 	Action action_prev;                  /* last operator action used by the repeat (dot) command */
 	Mode *mode;                          /* currently active mode, used to search for keybindings */

vis-lua.c

@@ -135,12 +135,16 @@ static void stack_dump(lua_State *L, const char *format, ...) {
 
 static int error_function(lua_State *L) {
 	Vis *vis = lua_touserdata(L, lua_upvalueindex(1));
+	if (vis->errorhandler)
+		return 1;
+	vis->errorhandler = true;
 	size_t len;
 	const char *msg = lua_tostring(L, 1);
 	if (msg)
 		luaL_traceback(L, L, msg, 1);
 	msg = lua_tolstring(L, 1, &len);
 	vis_message_show(vis, msg);
+	vis->errorhandler = false;
 	return 1;
 }