bolt11: fix amount encoding for large values

electrum/lnaddr.py

@@ -32,12 +32,14 @@ def shorten_amount(amount):
     """
     # Convert to pico initially
     amount = int(amount * 10**12)
-    units = ['p', 'n', 'u', 'm', '']
+    units = ['p', 'n', 'u', 'm']
     for unit in units:
         if amount % 1000 == 0:
             amount //= 1000
         else:
             break
+    else:
+        unit = ''
     return str(amount) + unit
 
 def unshorten_amount(amount) -> Decimal:

electrum/tests/test_bolt11.py

@@ -28,10 +28,11 @@ class TestBolt11(ElectrumTestCase):
             Decimal(123)/10**6: '123u',
             Decimal(123)/1000: '123m',
             Decimal(3): '3',
+            Decimal(1000): '1000',
         }
 
         for i, o in tests.items():
-            assert shorten_amount(i) == o
+            self.assertEqual(shorten_amount(i), o)
             assert unshorten_amount(shorten_amount(i)) == i
 
     @staticmethod