payment requests: fix explicit "None" expiration

Traceback (most recent call last):
  File "...\electrum\electrum\gui\qt\main_window.py", line 994, in <lambda>
    self.create_invoice_button.clicked.connect(lambda: self.create_invoice(False))
  File "...\electrum\electrum\gui\qt\main_window.py", line 1123, in create_invoice
    key = self.create_bitcoin_request(amount, message, expiry)
  File "...\electrum\electrum\gui\qt\main_window.py", line 1132, in create_bitcoin_request
    addr = self.wallet.get_unused_address()
  File "...\electrum\electrum\wallet.py", line 1452, in wrapper
    addr = func(self, *args, **kwargs)
  File "...\electrum\electrum\wallet.py", line 1465, in get_unused_address
    addrs = self.get_unused_addresses()
  File "...\electrum\electrum\wallet.py", line 1459, in get_unused_addresses
    in_use_by_request = [k for k in self.receive_requests.keys() if self.get_request_status(k)[0] != PR_EXPIRED]
  File "...\electrum\electrum\wallet.py", line 1459, in <listcomp>
    in_use_by_request = [k for k in self.receive_requests.keys() if self.get_request_status(k)[0] != PR_EXPIRED]
  File "...\electrum\electrum\wallet.py", line 1535, in get_request_status
    if exp > 0 and time.time() > timestamp + exp:
TypeError: '>' not supported between instances of 'NoneType' and 'int'

electrum/gui/qt/request_list.py

@@ -117,7 +117,6 @@ class RequestList(MyTreeView):
                 continue
             request_type = req['type']
             timestamp = req.get('time', 0)
-            expiration = req.get('exp', 0)
             amount = req.get('amount')
             message = req.get('message') or req.get('memo')
             date = format_time(timestamp)

electrum/util.py

@@ -113,7 +113,7 @@ pr_expiration_values = {
 
 def get_request_status(req):
     status = req['status']
-    exp = req.get('exp', 0)
+    exp = req.get('exp', 0) or 0
     if req['status'] == PR_UNPAID and exp > 0 and req['time'] + req['exp'] < time.time():
         status = PR_EXPIRED
     status_str = pr_tooltips[status]

electrum/wallet.py

@@ -1529,7 +1529,7 @@ class Abstract_Wallet(AddressSynchronizer, ABC):
         timestamp = r.get('time', 0)
         if timestamp and type(timestamp) != int:
             timestamp = 0
-        exp = r.get('exp', 0)
+        exp = r.get('exp', 0) or 0
         paid, conf = self.get_payment_status(address, amount)
         if not paid:
             if exp > 0 and time.time() > timestamp + exp: