hw_wallet: don't make watching only if cannot pair

Instead issue a warning.  Being watching-only disables
various functionality that should instead just ask again
for the PIN to be input.

lib/plugins.py

@@ -392,14 +392,22 @@ class DeviceMgr(PrintError):
             # See comment above for same code
             client.handler = wallet.handler
             # This will trigger a PIN/passphrase entry request
-            client_first_address = client.first_address(derivation)
+            try:
+                client_first_address = client.first_address(derivation)
+            except (UserCancelled, RuntimeError):
+                 # Bad / cancelled PIN / passphrase
+                client_first_address = None
             if client_first_address == first_address:
                 self.pair_wallet(wallet, info.device.id_)
                 return client
 
-        # The user input has wrong PIN or passphrase, or it is not pairable
+        # The user input has wrong PIN or passphrase, or cancelled input,
+        # or it is not pairable
         raise DeviceUnpairableError(
-            _('Unable to pair with your %s.') % plugin.device)
+            _('Unable to pair with your %s.\n\n'
+              'Ensure you are able to pair it, or you have the seed phrase, '
+              'before you request bitcoins to be sent to this wallet.'
+            ) % plugin.device)
 
     def unpaired_device_infos(self, handler, plugin, devices=None):
         '''Returns a list of DeviceInfo objects: one for each connected,