Do not popup snippets based on editor text
Kate currently shows the snippets popup when the user enter characters like '.' or '->' on a blank new line. The documentation (https://docs.kde.org/stable5/en/kate/kate/kate-application-plugin-snippets.html) specifies the popup should only appear by choosing it or via CTRL-SPACE. This fix overrides the default implementation of shouldStartCompletion so the pop up is no longer based on editor text.
The idea for this patch comes from a Reddit user's comment linked by the bug report (u/mTUX2).