trezor pin dialog: only show PIN "strength" when creating/changing

fixes #4832

electrum/plugins/keepkey/clientbase.py

@@ -1,5 +1,6 @@
 import time
 from struct import pack
+from typing import Optional
 
 from electrum import ecc
 from electrum.i18n import _
@@ -7,11 +8,12 @@ from electrum.util import UserCancelled
 from electrum.keystore import bip39_normalize_passphrase
 from electrum.bip32 import BIP32Node, convert_bip32_path_to_list_of_uint32
 from electrum.logging import Logger
-from electrum.plugins.hw_wallet.plugin import HardwareClientBase
+from electrum.plugins.hw_wallet.plugin import HardwareClientBase, HardwareHandlerBase
 
 
 class GuiMixin(object):
     # Requires: self.proto, self.device
+    handler: Optional[HardwareHandlerBase]
 
     messages = {
         3: _("Confirm the transaction output on your {} device"),
@@ -45,6 +47,7 @@ class GuiMixin(object):
         return self.proto.ButtonAck()
 
     def callback_PinMatrixRequest(self, msg):
+        show_strength = True
         if msg.type == 2:
             msg = _("Enter a new PIN for your {}:")
         elif msg.type == 3:
@@ -52,7 +55,8 @@ class GuiMixin(object):
                      "NOTE: the positions of the numbers have changed!"))
         else:
             msg = _("Enter your current {} PIN:")
-        pin = self.handler.get_pin(msg.format(self.device))
+            show_strength = False
+        pin = self.handler.get_pin(msg.format(self.device), show_strength=show_strength)
         if len(pin) > 9:
             self.handler.show_error(_('The PIN cannot be longer than 9 characters.'))
             pin = ''  # to cancel below