a_dbus_convert_value(): Be less strict about wrong strings

The code doesn't check the type of any of the values that it converts. However,
string elements are silently skipped if they cannot be converted.

The proper fix would be to make this code check types. For now, it will be ok to
"convert" non-strings to an empty string.

Signed-off-by: Uli Schlachter <psychon@znc.in>

dbus.c

@@ -319,7 +319,8 @@ a_dbus_convert_value(lua_State *L, int idx, DBusMessageIter *iter)
       case dbustype: \
         { \
             const char *s = lua_tostring(L, idx + 1); \
-            if(s) \
+            if(!s) \
+                s = ""; \
             dbus_message_iter_append_basic(iter, dbustype, &s); \
         } \
         break;