wallet.can_have_lightning: more explicit impl

Watching-only wallets can have a keystore.
It was actually keystore.may_have_password() that was filtering them out but that was not really obvious.
Better to be explicit I think.

electrum/wallet.py

@@ -521,9 +521,10 @@ class Abstract_Wallet(ABC, Logger, EventListener):
         if not self.txin_type == 'p2wpkh':
             return False
         if self.config.ENABLE_ANCHOR_CHANNELS:
-            # exclude watching-only wallets
             if not self.keystore:
                 return False
+            if self.keystore.is_watching_only():
+                return False
             # exclude hardware wallets
             if not self.keystore.may_have_password():
                 return False