use default modifiers if that's all we've got

xpra/x11/server_keyboard_config.py

@@ -18,7 +18,7 @@
 from xpra.gtk_common.keymap import get_gtk_keymap
 from xpra.gtk_common.gtk_util import get_default_root_window
 from xpra.gtk_common.error import xsync, xlog
-from xpra.keyboard.mask import DEFAULT_MODIFIER_NUISANCE, DEFAULT_MODIFIER_NUISANCE_KEYNAMES, mask_to_names
+from xpra.keyboard.mask import DEFAULT_MODIFIER_NUISANCE, DEFAULT_MODIFIER_MEANINGS, DEFAULT_MODIFIER_NUISANCE_KEYNAMES, mask_to_names
 from xpra.server.keyboard_config_base import KeyboardConfigBase
 from xpra.x11.gtk_x11.keys import grok_modifier_map
 from xpra.x11.xkbhelper import (
@@ -225,8 +225,8 @@ def compute_modifiers(self) -> None:
                 if MAP_MISSING_MODIFIERS:
                     map_missing_modifiers(self.keynames_for_mod)
             else:
-                log.info("client did not supply any modifier definitions")
-                self.keynames_for_mod = {}
+                log.info("client did not supply any modifier definitions, using defaults")
+                self.keynames_for_mod = get_modifiers_from_meanings(DEFAULT_MODIFIER_MEANINGS)
         log("compute_modifiers() keynames_for_mod=%s", self.keynames_for_mod)
         log("compute_modifiers() keycodes_for_modifier_keynames=%s", self.keycodes_for_modifier_keynames)
         log("compute_modifiers() mod_meanings=%s", self.mod_meanings)