kivy: minor fixes related to exchange rates

gui/kivy/main_window.py

@@ -179,8 +179,10 @@ class ElectrumWindow(App):
     def btc_to_fiat(self, amount_str):
         if not amount_str:
             return ''
+        if not self.fx.is_enabled():
+            return ''
         rate = self.fx.exchange_rate()
-        if not rate:
+        if rate.is_nan():
             return ''
         fiat_amount = self.get_amount(amount_str + ' ' + self.base_unit) * rate / pow(10, 8)
         return "{:.2f}".format(fiat_amount).rstrip('0').rstrip('.')
@@ -189,7 +191,7 @@ class ElectrumWindow(App):
         if not fiat_amount:
             return ''
         rate = self.fx.exchange_rate()
-        if not rate:
+        if rate.is_nan():
             return ''
         satoshis = int(pow(10,8) * Decimal(fiat_amount) / Decimal(rate))
         return format_satoshis_plain(satoshis, self.decimal_point())

gui/kivy/uix/dialogs/amount_dialog.py

@@ -39,6 +39,7 @@ Builder.load_string('''
                     size_hint: 1, None
                     font_size: '20dp'
                     height: '48dp'
+                    disabled: not app.fx.is_enabled()
                     on_release:
                         kb.is_fiat = True
             Widget:

gui/kivy/uix/dialogs/fx_dialog.py

@@ -106,4 +106,6 @@ class FxDialog(Factory.Popup):
             if ccy != self.fx.get_currency():
                 self.fx.set_currency(ccy)
             self.app.fiat_unit = ccy
+        else:
+            self.app.is_fiat = False
         Clock.schedule_once(lambda dt: self.add_exchanges())

gui/kivy/uix/screens.py

@@ -373,6 +373,8 @@ class ReceiveScreen(CScreen):
 
     def save_request(self):
         addr = self.screen.address
+        if not addr:
+            return
         amount = self.screen.amount
         message = self.screen.message
         amount = self.app.get_amount(amount) if amount else 0

gui/kivy/uix/ui_screens/history.kv

@@ -63,7 +63,7 @@ HistoryScreen:
             font_size: '30dp'
             bold: True
             size_hint: 1, 0.25
-            on_release: app.is_fiat = not app.is_fiat
+            on_release: app.is_fiat = not app.is_fiat if app.fx.is_enabled() else False
         ScrollView:
             id: content
             do_scroll_x: False