fix(completion): update 'completionItem/resolve' to always fall back

Details:
- Currently the 'completionItem/resolve' response falls back on the
  original LSP item only in case there was an explicit error. Which is a
  reasonable expectation (either error or response is not `nil`), but it
  seems to not be the case for some servers (and even not really a
  violation of the strict interpretation of the LSP specification).

  As 'completionItem/resolve' is a request that is intended to update
  an LSP completion item (used as argument), it is natural to always
  try to use it if the server didn't return its updated variant (for
  whatever reason).

Resolve #2090
Resolve #1991 (probably)

Author: echasnovski

lua/mini/completion.lua

@@ -1516,8 +1516,8 @@ H.info_window_lines = function(info_id)
     -- Do nothing if completion item was changed
     if H.info.id ~= info_id then return end
 
-    -- Still use original item if there was error during resolve
-    if err ~= nil then result = result or lsp_data.item end
+    -- Still use original item if there was no response (usually due to error)
+    result = result or lsp_data.item
 
     H.info.lsp.result = result
     -- - Cache resolved item to not have to send same request on revisit.