scratchtoolpp.cc: check return value of getchar()

CID 716865 (#1 of 1): Unchecked return value from library (CHECKED_RETURN)
 1. check_return: Calling function "getchar()" without checking return
  value. This library function may fail and return an error code.
 2. unchecked_value: No check of the return value of "getchar()"

Check really for 'enter' as the user asked for.

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>