fix: Error codes

# Check free diskspace

SPACE=$(df --output=avail -B 1 "$TMP" | tail -n 1)

SPACE_GB=$(( (SPACE + 1073741823)/1073741824 ))

(( SYSTEM_SIZE > SPACE )) && error "Not enough free space to create a 4 GB system disk, have only $SPACE_GB GB available." && exit 87

(( SYSTEM_SIZE > SPACE )) && error "Not enough free space to create a 4 GB system disk, have only $SPACE_GB GB available." && exit 97

if ! fallocate -l "$SYSTEM_SIZE" "$SYSTEM"; then

  if ! truncate -s "$SYSTEM_SIZE" "$SYSTEM"; then

    rm -f "$SYSTEM" && error "Could not allocate a file for the system disk." && exit 88

    rm -f "$SYSTEM" && error "Could not allocate a file for the system disk." && exit 98

  fi

fi

# Check if file exists

[ ! -f "$SYSTEM" ] && error "System disk does not exist ($SYSTEM)" && exit 89

[ ! -f "$SYSTEM" ] && error "System disk does not exist ($SYSTEM)" && exit 99

# Check the filesize

SIZE=$(stat -c%s "$SYSTEM")