margin calculation should allow for end-of-line indicator (#199)

* margin calculation should allow for end-of-line indicator

In whitespace mode, the end of line marker adds am extra char.

This should probably be detected via the approriate (if ..), but I
have no idea how.

Closes emacs-lsp/lsp-mode#499

* Test for whitespace mode, reduce margin if so

Author: alanz

lsp-ui-sideline.el

@@ -247,6 +247,9 @@ CURRENT is non-nil when the point is on the symbol."
          0)
      (if (bound-and-true-p display-line-numbers-mode)
          (+ 2 (line-number-display-width))
+       0)
+     (if (bound-and-true-p whitespace-mode)
+         1
        0)))
 
 (defun lsp-ui-sideline--window-width ()