qt fx settings: restore selected exchange in combobox if list changes

electrum/gui/qt/main_window.py

@@ -662,7 +662,6 @@ class ElectrumWindow(QMainWindow, MessageBoxMixin, PrintError):
             self.require_fee_update = False
         self.notify_transactions()
 
-
     def format_amount(self, x, is_diff=False, whitespaces=False):
         return format_satoshis(x, self.num_zeros, self.decimal_point, is_diff=is_diff, whitespaces=whitespaces)
 
@@ -2936,9 +2935,11 @@ class ElectrumWindow(QMainWindow, MessageBoxMixin, PrintError):
                 exchanges = self.fx.get_exchanges_by_ccy(c, h)
             else:
                 exchanges = self.fx.get_exchanges_by_ccy('USD', False)
+            ex_combo.blockSignals(True)
             ex_combo.clear()
             ex_combo.addItems(sorted(exchanges))
             ex_combo.setCurrentIndex(ex_combo.findText(self.fx.config_exchange()))
+            ex_combo.blockSignals(False)
 
         def on_currency(hh):
             if not self.fx: return