byteain for new hex escaped data

Looking at how byteain detects whether the input it is passed is the new 
hex format escape or the old octal escape, it uses:
        char       *inputText = PG_GETARG_CSTRING(0);        if (inputText[0] == '\\' && inputText[1] == 'x')

Doesn't this read off the end of inputText in the case of "SELECT 
''::bytea", or is there some padding happening somewhere that makes this 
legal?

Kris Jurka