[BUGFIX] Detection of curlProxyServer settings is incorrect

Parsing of 'curlProxyServer' option during the bootstrap is incorrect.
It produces wrong host and port part in 'proxy_host' and 'proxy_port'
system options.

Change-Id: I12f66acef697dbec9b065edcba8ad0d8f78c4e01
Resolves: #45834
Releases: 6.2, 6.1, 6.0
Reviewed-on: https://review.typo3.org/18481
Reviewed-by: Stefan Neufeind
Tested-by: Stefan Neufeind
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters