Tweak some details, fix some bugs

Tweak some details, fix some bugs

eglot--recover-workspace-symbol-meta had a bug that still made it
choke on improper lists.

Also, when simply M-. to the thing at point, let's not lose time on
iterating a potentially out-of-date eglot--workspace-symbols-cache.
So clear it early in the pre-command-hook.

* eglot.el (eglot--workspace-symbols-cache): Move up.
(eglot--pre-command-hook): Clear eglot--workspace-symbols-cache here.
(eglot--recover-workspace-symbol-meta): Check for consp.

GitHub-reference: per https://github.com/joaotavora/eglot/issues/131