fix(events): don't expand non-file as file name

src/nvim/autocmd.c

@@ -1676,6 +1676,7 @@ bool apply_autocmds_group(event_T event, char *fname, char *fname_io, bool force
         || event == EVENT_USER || event == EVENT_WINCLOSED
         || event == EVENT_WINRESIZED || event == EVENT_WINSCROLLED) {
       fname = xstrdup(fname);
+      autocmd_fname_full = true;  // don't expand it later
     } else {
       fname = FullName_save(fname, false);
     }

src/nvim/path.c

@@ -2087,17 +2087,17 @@ char *path_shorten_fname(char *full_path, char *dir_name)
   assert(dir_name != NULL);
   size_t len = strlen(dir_name);
 
-  // If dir_name is a path head, full_path can always be made relative.
-  if (len == (size_t)path_head_length() && is_path_head(dir_name)) {
-    return full_path + len;
-  }
-
   // If full_path and dir_name do not match, it's impossible to make one
   // relative to the other.
   if (path_fnamencmp(dir_name, full_path, len) != 0) {
     return NULL;
   }
 
+  // If dir_name is a path head, full_path can always be made relative.
+  if (len == (size_t)path_head_length() && is_path_head(dir_name)) {
+    return full_path + len;
+  }
+
   char *p = full_path + len;
 
   // If *p is not pointing to a path separator, this means that full_path's