CLI: fix regression re handling "unknown command", re locale

if qt is not installed, e.g. on a server, was getting:
```
$ ./run_electrum sadasdasddsa
Traceback (most recent call last):
  File "/home/user/wspace/electrum/./run_electrum", line 532, in <module>
    main()
  File "/home/user/wspace/electrum/./run_electrum", line 383, in main
    lang = get_default_language(gui_name=gui_name)
  File "/home/user/wspace/electrum/electrum/gui/default_lang.py", line 23, in get_default_language
    from PyQt5.QtCore import QLocale
ModuleNotFoundError: No module named 'PyQt5.QtCore'
```

run_electrum

@@ -376,12 +376,15 @@ def main():
     # Note: it is ok to call set_language() again later, but note that any call only applies
     #       to not-yet-evaluated strings.
     if cmdname == 'gui':
-        from electrum.gui.default_lang import get_default_language
         gui_name = config.GUI_NAME
         lang = config.LOCALIZATION_LANGUAGE
         if not lang:
-            lang = get_default_language(gui_name=gui_name)
-            _logger.info(f"get_default_language: detected default as {lang=!r}")
+            try:
+                from electrum.gui.default_lang import get_default_language
+                lang = get_default_language(gui_name=gui_name)
+                _logger.info(f"get_default_language: detected default as {lang=!r}")
+            except ImportError as e:
+                _logger.info(f"get_default_language: failed. got exc={e!r}")
         set_language(lang)
 
     if config.get('testnet'):