qt: handle exceptions when pressing "Max" button

fixes #5783

electrum/gui/qt/channels_list.py

@@ -6,7 +6,7 @@ from PyQt5 import QtCore, QtGui
 from PyQt5.QtCore import Qt
 from PyQt5.QtWidgets import QMenu, QHBoxLayout, QLabel, QVBoxLayout, QGridLayout, QLineEdit
 
-from electrum.util import bh2u
+from electrum.util import bh2u, NotEnoughFunds, NoDynamicFeeEstimates
 from electrum.i18n import _
 from electrum.lnchannel import Channel
 from electrum.wallet import Abstract_Wallet
@@ -178,7 +178,13 @@ class ChannelsList(MyTreeView):
             if not max_button.isChecked():
                 return
             make_tx = self.parent.mktx_for_open_channel('!')
-            tx = make_tx(None)
+            try:
+                tx = make_tx(None)
+            except (NotEnoughFunds, NoDynamicFeeEstimates) as e:
+                max_button.setChecked(False)
+                amount_e.setFrozen(False)
+                self.main_window.show_error(str(e))
+                return
             amount = tx.output_value()
             amount = min(amount, LN_MAX_FUNDING_SAT)
             amount_e.setAmount(amount)

electrum/gui/qt/main_window.py

@@ -60,7 +60,8 @@ from electrum.util import (format_time, format_satoshis, format_fee_satoshis,
                            decimal_point_to_base_unit_name,
                            UnknownBaseUnit, DECIMAL_POINT_DEFAULT, UserFacingException,
                            get_new_wallet_name, send_exception_to_crash_reporter,
-                           InvalidBitcoinURI, maybe_extract_bolt11_invoice)
+                           InvalidBitcoinURI, maybe_extract_bolt11_invoice, NotEnoughFunds,
+                           NoDynamicFeeEstimates)
 from electrum.util import PR_TYPE_ONCHAIN, PR_TYPE_LN
 from electrum.transaction import (Transaction, PartialTxInput,
                                   PartialTransaction, PartialTxOutput)
@@ -1293,14 +1294,20 @@ class ElectrumWindow(QMainWindow, MessageBoxMixin, Logger):
         outputs = self.payto_e.get_outputs(True)
         if not outputs:
             return
-        self.max_button.setChecked(True)
         make_tx = lambda fee_est: self.wallet.make_unsigned_transaction(
             coins=self.get_coins(),
             outputs=outputs,
             fee=fee_est,
             is_sweep=False)
 
-        tx = make_tx(None)
+        try:
+            tx = make_tx(None)
+        except (NotEnoughFunds, NoDynamicFeeEstimates) as e:
+            self.max_button.setChecked(False)
+            self.show_error(str(e))
+            return
+
+        self.max_button.setChecked(True)
         amount = tx.output_value()
         __, x_fee_amount = run_hook('get_tx_extra_fee', self.wallet, tx) or (None, 0)
         amount_after_all_fees = amount - x_fee_amount