invoices: also run amount-validator on setter

- @amount_msat.validator prevents the creation of invoices with e.g. too large amounts
- however the qml gui is mutating invoices by directly setting the `amount_msat` field,
  and it looks like attrs validators only run during init.
  We can use `on_setattr` (introduced in attrs==20.1.0).
- a wallet db upgrade is added to rm existing insane invoices
- btw the qml gui was already doing its own input validation on the textedit
  (see qeconfig.btcAmountRegex). however that only limits the input to not have more
  chars than what is needed to represent 21M BTC (e.g. you can still enter 99M BTC,
  which the invoice logic does not tolerate later on - but is normally caught).

fixes https://github.com/spesmilo/electrum/issues/8582

electrum/wallet_db.py

@@ -54,7 +54,7 @@ from .version import ELECTRUM_VERSION
 
 OLD_SEED_VERSION = 4        # electrum versions < 2.0
 NEW_SEED_VERSION = 11       # electrum versions >= 2.0
-FINAL_SEED_VERSION = 53     # electrum >= 2.7 will set this to prevent
+FINAL_SEED_VERSION = 54     # electrum >= 2.7 will set this to prevent
                             # old versions from overwriting new format
 
 
@@ -239,6 +239,7 @@ class WalletDB(JsonDB):
         self._convert_version_51()
         self._convert_version_52()
         self._convert_version_53()
+        self._convert_version_54()
         self.put('seed_version', FINAL_SEED_VERSION)  # just to be sure
 
         self._after_upgrade_tasks()
@@ -1076,6 +1077,23 @@ class WalletDB(JsonDB):
                 cb['local_payment_pubkey'] = None
         self.data['seed_version'] = 53
 
+    def _convert_version_54(self):
+        # note: similar to convert_version_38
+        if not self._is_upgrade_method_needed(53, 53):
+            return
+        from .bitcoin import TOTAL_COIN_SUPPLY_LIMIT_IN_BTC, COIN
+        max_sats = TOTAL_COIN_SUPPLY_LIMIT_IN_BTC * COIN
+        requests = self.data.get('payment_requests', {})
+        invoices = self.data.get('invoices', {})
+        for d in [invoices, requests]:
+            for key, item in list(d.items()):
+                amount_msat = item['amount_msat']
+                if amount_msat == '!':
+                    continue
+                if not (isinstance(amount_msat, int) and 0 <= amount_msat <= max_sats * 1000):
+                    del d[key]
+        self.data['seed_version'] = 54
+
     def _convert_imported(self):
         if not self._is_upgrade_method_needed(0, 13):
             return