fixed bugs #3171768: makebin fails when data is at the last byte,
  #3171795: If makebin read_ihx fails, it should exit with an error code


git-svn-id: https://sdcc.svn.sourceforge.net/svnroot/sdcc/trunk/sdcc@6192 4a8a32a2-be11-0410-ad9d-d568d2c75423