Fix checking workspaceFolders in rHelpProviderOptions

[renkun-ken]

What problem did you solve?

Fix checking workspaceFolders in the initialization of the help panel.

(If you do not have screenshot) How can I check this pull request?

1. No open workspace folders.
2. Open or create an R file.
3. vscode-R should be activated properly.

[renkun-ken]

@Ikuyadeu We might need a quick release for this as the extension activation for no open workspace folder is broken.

[ManuelHentschel]

Would it make sense to also check the length of the array?

         cwd: ((workspace.workspaceFolders !== undefined && workspace.workspaceFolders.length > 0) ? workspace.workspaceFolders[0].uri.fsPath : undefined)

The documentation seems to imply that an array of length 0 won't occurr ("List of workspace folders or undefined when no folder is open."), but better be safe than sorry

[renkun-ken]

@ManuelHentschel Agreed.

Note that both vscode-R and languageserver support multi-root workspace. We might revisit the code where workspaceFolders[0] is used and see how we could properly handle multi-root workspace in these cases.