The build would continue even if the some of the intermediate commands
failed, as long as the last command in the final iteration of the loop
was successful.
Add 'set -e' to the subshell so that we immediately exit. Previously,
only the exit status of the final make-index-json.py mattered.
Fixes: https://github.com/openwrt/openwrt/issues/21981
Signed-off-by: Matt Merhar <mattmerhar@protonmail.com>
Link: https://github.com/openwrt/openwrt/pull/21993
Signed-off-by: Robert Marko <robimarko@gmail.com>
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