Fixed search page-id edgecase

[corvin-koegler]

Adding a space to numeric searches prevents markdown from breaking the search.

Issue 612

[frcroth]

Can you explain why this happens?

[lukasrad02]

This only fixes the symptom, but not the actual root cause.

The underlying problem of #612 is that the highlighting logic replaces substrings in the markdown text. So, for example, searching for "page" also breaks our internal links (in the form of [Text](page:123)). This query does not cause a internal server error, as the markdown renderer just uses **page**:123 as link target, but it still alters the meaning.

Hence, we either have to use a more sophisticated highlighting logic (parsing the markdown into an AST, then performing replacements only on textnodes and then writing the AST back to markdown), or have to remove the highlighting completely.