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

doc/vimwiki.txt

@@ -3924,6 +3924,7 @@ Contributors and their Github usernames in roughly chronological order:
     - Vinny Furia (@vinnyfuria)
     - paperbenni (@paperbenni)
     - Lily Foster (@lilyinstarlight)
+    - Thomas Leyh (@leyhline)
 
 ==============================================================================
 16. Changelog                                              *vimwiki-changelog*
@@ -3994,6 +3995,7 @@ Changed:~
 Removed:~
 
 Fixed:~
+    * Issue #1193: Fix wildcard expansion in |find_autoload_file|
     * PR #1108: Fix resolution of leading-slash page links, add link tests
     * Allow title values with quotes
     * Enable strikethrough for Neovim