qt tx dialog: small fee edit fix

scenario: enter extremely high feerate (which we cannot satisfy) then click into fee_edit.
At that moment, fee_edit is empty and both feerate_edit and fee_edit are considered frozen.
As fee_edit has priority, we would construct a tx with default fee.
Now, instead, we won't construct this default fee tx ~as if the click to fee_edit did not happen.

electrum/gui/qt/amountedit.py

@@ -1,6 +1,7 @@
 # -*- coding: utf-8 -*-
 
 from decimal import Decimal
+from typing import Union
 
 from PyQt5.QtCore import pyqtSignal, Qt
 from PyQt5.QtGui import QPalette, QPainter
@@ -71,7 +72,7 @@ class AmountEdit(MyLineEdit):
             painter.setPen(self.help_palette.brush(QPalette.Disabled, QPalette.Text).color())
             painter.drawText(textRect, Qt.AlignRight | Qt.AlignVCenter, self.base_unit())
 
-    def get_amount(self):
+    def get_amount(self) -> Union[None, Decimal, int]:
         try:
             return (int if self.is_int else Decimal)(str(self.text()))
         except:

electrum/gui/qt/transaction_dialog.py

@@ -693,9 +693,9 @@ class PreviewTxDialog(BaseTxDialog, TxEditor):
                                  .format(num_satoshis_added))
 
     def get_fee_estimator(self):
-        if self.is_send_fee_frozen():
+        if self.is_send_fee_frozen() and self.fee_e.get_amount() is not None:
             fee_estimator = self.fee_e.get_amount()
-        elif self.is_send_feerate_frozen():
+        elif self.is_send_feerate_frozen() and self.feerate_e.get_amount() is not None:
             amount = self.feerate_e.get_amount()  # sat/byte feerate
             amount = 0 if amount is None else amount * 1000  # sat/kilobyte feerate
             fee_estimator = partial(

electrum/util.py

@@ -642,7 +642,7 @@ def format_fee_satoshis(fee, *, num_zeros=0, precision=None):
     return format_satoshis(fee, num_zeros=num_zeros, decimal_point=0, precision=precision)
 
 
-def quantize_feerate(fee):
+def quantize_feerate(fee) -> Union[None, Decimal, int]:
     """Strip sat/byte fee rate of excess precision."""
     if fee is None:
         return None