Don't try to read unreadable buffer

bufnr() can return a result for recently read files which are not loaded
in the current session. When this happens getbufline() will fail. Gate
the read with bufloaded.

CHANGELOG.md

@@ -4,6 +4,7 @@
 - Sort diagnostics in location list.
 - Allow only 1 server command per filetype.
 - Add commands for GoToDefinition and FindReferences
+- Bug fix: Don't try to read lines from unreadable buffer.
 
 # 0.1.3
 

autoload/lsc/reference.vim

@@ -69,10 +69,10 @@ function! s:QuickFixItem(location) abort
   let file_path = lsc#util#documentPath(a:location.uri)
   let item.filename = fnamemodify(file_path, ':~:.')
   let bufnr = bufnr(file_path)
-  if bufnr == -1
-    let item.text = readfile(file_path, '', item.lnum)[item.lnum - 1]
-  else
+  if bufnr != -1 && bufloaded(bufnr)
     let item.text = getbufline(bufnr, item.lnum)[0]
+  else
+    let item.text = readfile(file_path, '', item.lnum)[item.lnum - 1]
   endif
   return item
 endfunction