refactor error code handler to avoid possible string overflows and handle out of range argument

    int errorflag = 0;

    meam_inst->meam_setup_param(which,value,nindex,index,&errorflag);

    if (errorflag) {

      char str[128];

      snprintf(str,80,"Error in MEAM parameter file: keyword %s",params[0]);

      switch(errorflag) {

        case 1: strcat(str, " is out of range (please report a bug)"); break;

        case 2: strcat(str, " expected more indices"); break;

        case 3: strcat(str, " has out of range element index"); break;

      }

      const char *descr[] = { "has an unknown error",

              "is out of range (please report a bug)",

              "expected more indices",

              "has out of range element index"};

      char str[256];

      if ((errorflag < 0) || (errorflag > 3)) errorflag = 0;

      snprintf(str,256,"Error in MEAM parameter file: keyword %s %s",params[0],descr[errorflag]);

      error->all(FLERR,str);

    }

  }

  delete [] params;

}