define frozen signal for exchange rate plugin

gui/qt/amountedit.py

@@ -6,10 +6,12 @@ from PyQt4.QtGui import *
 from decimal import Decimal
 
 class MyLineEdit(QLineEdit):
+    frozen = pyqtSignal()
 
     def setFrozen(self, b):
         self.setReadOnly(b)
         self.setFrame(not b)
+        self.frozen.emit()
 
 class AmountEdit(MyLineEdit):
 

gui/qt/main_window.py

@@ -872,6 +872,7 @@ class ElectrumWindow(QMainWindow):
                 fee = self.wallet.estimated_fee(inputs, 1)
                 amount = total - fee
                 self.amount_e.setAmount(amount)
+                self.amount_e.textEdited.emit("")
                 self.fee_e.setAmount(fee)
                 return
 

gui/qt/paytoedit.py

@@ -123,6 +123,8 @@ class PayToEdit(QRTextEdit):
         else:
             self.amount_edit.setText("")
 
+        self.amount_edit.textEdited.emit("")
+
         if total or len(lines)>1:
             self.lock_amount()
         else:

plugins/exchange_rate.py

@@ -661,4 +661,5 @@ class Plugin(BasePlugin):
             if fiat_amount is not None:
                 self.fiat_e.setText("%.2f"%fiat_amount)
         self.btc_e.textEdited.connect(btc_changed)
+        self.btc_e.frozen.connect(lambda: self.fiat_e.setFrozen(self.btc_e.isReadOnly()))
         self.win.send_grid.addWidget(self.fiat_e, 4, 3, Qt.AlignHCenter)