Fix ledger sign message (#7004)

there was an around ~1/128 chance of creating an invalid signature when signing a message with a ledger

electrum/plugins/ledger/ledger.py

@@ -334,7 +334,12 @@ class Ledger_KeyStore(Hardware_KeyStore):
         if sLength == 33:
             s = s[1:]
         # And convert it
-        return bytes([27 + 4 + (signature[0] & 0x01)]) + r + s
+
+        # Pad r and s points with 0x00 bytes when the point is small to get valid signature.
+        r_padded = bytes([0x00]) * (32 - len(r)) + r
+        s_padded = bytes([0x00]) * (32 - len(s)) + s
+        
+        return bytes([27 + 4 + (signature[0] & 0x01)]) + r_padded + s_padded
 
     @runs_in_hwd_thread
     @test_pin_unlocked