lsp-format-region: Fix error "no region"

[sunlin7]

The lsp-format-region will emit error message The mark is not set now, so there is no region at the very beginning.
It can be reproduced with follow steps:
Start the Emacs with lsp, and open a c++ file /tmp/a.cpp, and execute lsp-format-region, then got the error message.

To workaround the issue, just select one char/word and de-select the region, then execute the lsp-format-region.

This PR will follow the document of lsp-format-region description to accept region or line.

Please help review and approve this change, thanks

[jcs090218]

Isn't that the expected behaviour? 🤔 lsp-format-region without selecting a region isn't allowed.

[sunlin7]

@jcs090218
No. The document of lsp-format-region says it should be current line when no region been selected:
Ask the server to format the region, or if none is selected, the current line.