Fix wildcard expansion in find_autoload_file

When using vim's native mechanism for `packages`, wildcards (*) are used
in the `runtimepath` since package folders can have arbitrary names.
They were not expanded, thus a path to e.g. `default.tpl` could not be
resolved when calling Vimwiki2HTML.

Resolves vimwiki/vimwiki#1193

autoload/vimwiki/html.vim

@@ -87,8 +87,9 @@ endfunction
 function! s:find_autoload_file(name) abort
   for path in split(&runtimepath, ',')
     let fname = path.'/autoload/vimwiki/'.a:name
-    if glob(fname) !=? ''
-      return fname
+    let match = glob(fname)
+    if match !=? ''
+      return match
     endif
   endfor
   return ''