app/compose: Reorder logic around treefile parsing

Move up the setting of the treefile JSON object to right after parsing,
and move down the populating of the metadata hash table to after setting
the treefile JSON object. This is pure code block moves; there's no
functional change otherwise.

Prep for future patch.

Closes: #1865
Approved by: cgwalters

src/app/rpmostree-compose-builtin-tree.c

@@ -682,21 +682,6 @@ rpm_ostree_compose_context_new (const char    *treefile_pathstr,
 
   self->treefile_path = g_file_new_for_path (treefile_pathstr);
 
-  self->metadata = g_hash_table_new_full (g_str_hash, g_str_equal, g_free,
-                                          (GDestroyNotify)g_variant_unref);
-  if (opt_metadata_json)
-    {
-      if (!rpmostree_composeutil_read_json_metadata_from_file (opt_metadata_json,
-                                                               self->metadata, error))
-        return FALSE;
-    }
-
-  if (opt_metadata_strings)
-    {
-      if (!parse_metadata_keyvalue_strings (opt_metadata_strings, self->metadata, error))
-        return FALSE;
-    }
-
   self->corectx = rpmostree_context_new_tree (self->cachedir_dfd, self->build_repo,
                                               cancellable, error);
   if (!self->corectx)
@@ -718,6 +703,27 @@ rpm_ostree_compose_context_new (const char    *treefile_pathstr,
                                error))
     return FALSE;
 
+  self->treefile_rootval = json_parser_get_root (self->treefile_parser);
+  if (!JSON_NODE_HOLDS_OBJECT (self->treefile_rootval))
+    return glnx_throw (error, "Treefile root is not an object");
+
+  self->treefile = json_node_get_object (self->treefile_rootval);
+
+  self->metadata = g_hash_table_new_full (g_str_hash, g_str_equal, g_free,
+                                          (GDestroyNotify)g_variant_unref);
+  if (opt_metadata_json)
+    {
+      if (!rpmostree_composeutil_read_json_metadata_from_file (opt_metadata_json,
+                                                               self->metadata, error))
+        return FALSE;
+    }
+
+  if (opt_metadata_strings)
+    {
+      if (!parse_metadata_keyvalue_strings (opt_metadata_strings, self->metadata, error))
+        return FALSE;
+    }
+
   g_auto(GStrv) layers = ror_treefile_get_all_ostree_layers (self->treefile_rs);
   if (layers && *layers && !opt_unified_core)
     return glnx_throw (error, "ostree-layers requires unified-core mode");
@@ -733,10 +739,6 @@ rpm_ostree_compose_context_new (const char    *treefile_pathstr,
         }
     }
 
-  self->treefile_rootval = json_parser_get_root (self->treefile_parser);
-  if (!JSON_NODE_HOLDS_OBJECT (self->treefile_rootval))
-    return glnx_throw (error, "Treefile root is not an object");
-  self->treefile = json_node_get_object (self->treefile_rootval);
   self->treespec = rpmostree_composeutil_get_treespec (self->corectx,
                                                        self->treefile_rs,
                                                        self->treefile,