lnworker.invoices access now uses lock

(qt gui thread vs asyncio thread race)

Traceback (most recent call last):
  File "/home/user/wspace/electrum/electrum/gui/qt/main_window.py", line 1685, in do_send
    self.pay_lightning_invoice(self.payto_e.lightning_invoice)
  File "/home/user/wspace/electrum/electrum/gui/qt/main_window.py", line 1667, in pay_lightning_invoice
    self.invoice_list.update()
  File "/home/user/wspace/electrum/electrum/gui/qt/invoice_list.py", line 73, in update
    _list = self.parent.wallet.get_invoices()
  File "/home/user/wspace/electrum/electrum/wallet.py", line 525, in get_invoices
    out += self.lnworker.get_invoices()
  File "/home/user/wspace/electrum/electrum/util.py", line 401, in
    return lambda *args, **kw_args: do_profile(args, kw_args)
  File "/home/user/wspace/electrum/electrum/util.py", line 397, in do_profile
    o = func(*args, **kw_args)
  File "/home/user/wspace/electrum/electrum/lnworker.py", line 1007, in get_invoices
    for key, (invoice, direction, status) in self.invoices.items():
RuntimeError: dictionary changed size during iteration

electrum/lnworker.py

@@ -958,6 +958,7 @@ class LNWallet(LNWorker):
 
     def save_invoice(self, payment_hash:bytes, invoice, direction, status):
         key = bh2u(payment_hash)
+        with self.lock:
             self.invoices[key] = invoice, direction, status
         self.storage.put('lightning_invoices', self.invoices)
         self.storage.write()
@@ -1004,7 +1005,9 @@ class LNWallet(LNWorker):
     def get_invoices(self):
         # invoices = outgoing
         out = []
-        for key, (invoice, direction, status) in self.invoices.items():
+        with self.lock:
+            invoice_items = list(self.invoices.items())
+        for key, (invoice, direction, status) in invoice_items:
             if direction == SENT and status != PR_PAID:
                 out.append(self.get_request(key))
         return out
@@ -1013,7 +1016,9 @@ class LNWallet(LNWorker):
     def get_requests(self):
         # requests = incoming
         out = []
-        for key, (invoice, direction, status) in self.invoices.items():
+        with self.lock:
+            invoice_items = list(self.invoices.items())
+        for key, (invoice, direction, status) in invoice_items:
             if direction == RECEIVED and status != PR_PAID:
                 out.append(self.get_request(key))
         return out
@@ -1062,6 +1067,7 @@ class LNWallet(LNWorker):
 
     def delete_invoice(self, payment_hash_hex: str):
         try:
+            with self.lock:
                 del self.invoices[payment_hash_hex]
         except KeyError:
             return