digitalbitbox: correctly handle user aborts

1. When the pairing is being forced and the user clicks 'No', the tx
was cancelled completely because the UserCancelled exception was
accidentally converted to an Exception.
2. Same with user aborting the signing process with a short touch on
the device (or a timeout).

plugins/digitalbitbox/digitalbitbox.py

@@ -11,7 +11,7 @@ try:
     from electrum.i18n import _
     from electrum.keystore import Hardware_KeyStore
     from ..hw_wallet import HW_PluginBase
-    from electrum.util import print_error, to_string
+    from electrum.util import print_error, to_string, UserCancelled
 
     import time
     import hid
@@ -588,6 +588,9 @@ class DigitalBitbox_KeyStore(Hardware_KeyStore):
                 self.handler.finished()
 
                 if 'error' in reply:
+                    if reply["error"].get('code') in (600, 601):
+                        # aborted via LED short touch or timeout
+                        raise UserCancelled()
                     raise Exception(reply['error']['message'])
 
                 if 'sign' not in reply:
@@ -623,6 +626,8 @@ class DigitalBitbox_KeyStore(Hardware_KeyStore):
                     sig = sigencode_der(sig_r, sig_s, generator_secp256k1.order())
                     txin['signatures'][ii] = to_hexstr(sig) + '01'
                     tx._inputs[i] = txin
+        except UserCancelled:
+            raise
         except BaseException as e:
             self.give_error(e, True)
         else: