[BUGFIX] Show error messages when debugging is enabled

scheduler_http calls typo3/cli_dispatch.sh, captures its output and
displays that output when debugging is enabled.

It does not catch messages on stderr, thus making it impossible to
find out the reason for errors with the scheduler.

Fixes: #45288
Merge pull request #1 from netresearch/TYPO-58

[BUGFIX] Show error messages when debugging is enabled