fix(syslog): return early when logger init fails

[bhuvan-somisetty]

Description

send_syslog_data() in apisix/plugins/syslog/init.lua fetches the logger instance from the lrucache and correctly checks whether it failed:

if not logger then
res = false
err_msg = "failed when initiating the sys logger processor".. err
end

When logger_socket.new(...) fails, for example due to a bad host or port or a socket error, logger is nil and this branch correctly builds an error message, but it never returns. Execution falls through to the very next line, logger:log(log_message), which indexes a nil value. This throws an uncaught Lua runtime error inside the log phase batch processor callback instead of returning the already built false, err_msg back to the caller, the same way the function already does for the logger:log() failure case right below it.

This PR adds the missing return so a failed logger init is reported as a clean batch processor error instead of crashing the log phase.

Which issue(s) this PR fixes:

Fixes #13969

Checklist

• I have explained the need for this PR and the problem it solves
• I have explained the changes or the new features added to this PR
• I have added tests corresponding to this change
• I have updated the documentation to reflect this change (no user facing docs needed for this internal bug fix)
• I have verified that this change is backward compatible