Prolog & Lua: fix shebang

Summary: Before, the shebang was highlighted if there were empty lines before. Now it will only be highlighted in the first line.

Reviewers: Framework: Syntax Highlighting, cullmann, dhaumann

Reviewed By: Framework: Syntax Highlighting, cullmann

Subscribers: kwrite-devel, kde-frameworks-devel

Tags: Kate, Frameworks

Differential Revision: https://phabricator.kde.org/D17084