Exit status code in BEGIN should apply if END has exit

[benhoyt]

If there's an exit in the BEGIN block with an exit code, that status code should be returned, even if there's an exit in the END block with a zero exit code. For example:

$ goawk 'BEGIN { exit 23 }; END { exit }'; echo $?
0

All other AWKs print 23.

Thanks @raygard for the bug report.