Fix for issue #756.

[russtoku]

This PR should address Issue #756.

The initial error reported led to discovery of a problem with the completion function for the Scheme, Guile, and Common Lisp clients. As it turns out, the attempt to index local 'cursor_node' (a nil value) message was the key to finding a solution.

The main problem lies with not calling vim.treesitter.get_node before the buffer is parsed by the parser method on vim.treesitter.get_parser on the current buffer for the filetype of the buffer. Luckily, there is already code in place to help so it takes just one line to resolve this issue. Also, this change will fix three Conjure client because they all call get-completions-at-cursor in conjure.tree-sitter-completions.

L.3 and L.86 are the main fix. The other changes are cosmetic whitespace removal.

[Olical]

Makes sense! Tricky that we need to be aware of this every time we interact with tree sitter.