fix unrelated bug when fromStr input is short hex

For example, 0x0 will generate an unhandled ValueError. This was caught
during a random unit test run for 3.9, so I figure I'd fix it.

This is unrelated to the PR otherwise.

meshtastic/util.py

@@ -82,7 +82,7 @@ def fromStr(valstr):
         val = bytes()
     elif valstr.startswith("0x"):
         # if needed convert to string with asBytes.decode('utf-8')
-        val = bytes.fromhex(valstr[2:])
+        val = bytes.fromhex(valstr[2:].zfill(2))
     elif valstr.startswith("base64:"):
         val = base64.b64decode(valstr[7:])
     elif valstr.lower() in {"t", "true", "yes"}: