utils: fix double loop when extracting icons for appstream

When trying to extract icons to regenerate the appstream, we are looping
over the entire file every time, instead of only trying to copy icons
for the application ID we're looking at the moment.
This is most likely benign, but it causes a lot of "Error copying icon:
No such file or directory:" spew when calling flatpak build-update-repo.

common/flatpak-utils.c

@@ -2201,7 +2201,8 @@ extract_appstream (OstreeRepo   *repo,
           component_id_text_node = flatpak_xml_find (component_id, NULL, NULL);
 
           component_id_text = g_strstrip (g_strdup (component_id_text_node->text));
-          if (!g_str_has_suffix (component_id_text, ".desktop"))
+          if (!g_str_has_prefix (component_id_text, id) ||
+              !g_str_has_suffix (component_id_text, ".desktop"))
             {
               component = component->next_sibling;
               continue;
@@ -2221,7 +2222,8 @@ extract_appstream (OstreeRepo   *repo,
               g_clear_error (&my_error);
             }
 
-          component = component->next_sibling;
+          /* We updated icons for our component, so we're done */
+          break;
         }
     }