bertlv_parse_len: Fix input data is smaller than num length octets

This can happen if there's a file with invalid encoding on the card,
such as a tag followed by all-ff.  Let's gracefully ignore it and
return zero bytes as response.

Change-Id: Ic44557368a6034dbf4bb021ab23a57927c22def0

pySim/utils.py

@@ -314,6 +314,8 @@ def bertlv_parse_len(binary: bytes) -> Tuple[int, bytes]:
     else:
         num_len_oct = binary[0] & 0x7f
         length = 0
+        if len(binary) < num_len_oct + 1:
+            return (0, b'')
         for i in range(1, 1+num_len_oct):
             length <<= 8
             length |= binary[i]