lib/commit: fix using uninitialized var

Noticed this while reading the code. The `child` var hasn't been
initialized yet at the time we throw this error (and even then, it's
only conditionally initialized). To be nice, let's just always calculate
the child path and pass that along.

Also do some minor style porting to decl near use.

src/libostree/ostree-repo-commit.c

@@ -2496,23 +2496,16 @@ write_directory_content_to_mtree_internal (OstreeRepo                  *self,
                                            GCancellable                *cancellable,
                                            GError                     **error)
 {
-  g_autoptr(GFile) child = NULL;
-  g_autoptr(GFileInfo) modified_info = NULL;
-  g_autoptr(OstreeMutableTree) child_mtree = NULL;
-  g_autofree char *child_relpath = NULL;
-  const char *name;
-  GFileType file_type;
-  OstreeRepoCommitFilterResult filter_result;
-
   g_assert (dir_enum != NULL || dfd_iter != NULL);
 
-  name = g_file_info_get_name (child_info);
+  const char *name = g_file_info_get_name (child_info);
   g_ptr_array_add (path, (char*)name);
 
-  if (modifier != NULL)
-    child_relpath = ptrarray_path_join (path);
+  g_autofree char *child_relpath = ptrarray_path_join (path);
 
-  filter_result = _ostree_repo_commit_modifier_apply (self, modifier, child_relpath, child_info, &modified_info);
+  g_autoptr(GFileInfo) modified_info = NULL;
+  OstreeRepoCommitFilterResult filter_result =
+    _ostree_repo_commit_modifier_apply (self, modifier, child_relpath, child_info, &modified_info);
 
   if (filter_result != OSTREE_REPO_COMMIT_FILTER_ALLOW)
     {
@@ -2521,23 +2514,24 @@ write_directory_content_to_mtree_internal (OstreeRepo                  *self,
       return TRUE;
     }
 
-  file_type = g_file_info_get_file_type (child_info);
+  GFileType file_type = g_file_info_get_file_type (child_info);
   switch (file_type)
     {
     case G_FILE_TYPE_DIRECTORY:
     case G_FILE_TYPE_SYMBOLIC_LINK:
     case G_FILE_TYPE_REGULAR:
       break;
     default:
-      return glnx_throw (error, "Unsupported file type: '%s'",
-                         gs_file_get_path_cached (child));
+      return glnx_throw (error, "Unsupported file type for file: '%s'", child_relpath);
     }
 
+  g_autoptr(GFile) child = NULL;
   if (dir_enum != NULL)
     child = g_file_enumerator_get_child (dir_enum, child_info);
 
   if (file_type == G_FILE_TYPE_DIRECTORY)
     {
+      g_autoptr(OstreeMutableTree) child_mtree = NULL;
       if (!ostree_mutable_tree_ensure_dir (mtree, name, &child_mtree, error))
         return FALSE;