[cache] Fix error handling.

Manipulate the cache after a face is requested or a size is looked up
successfully. Fixes #1270.

* src/cache/ftcmanag.c (ftc_size_node_init, ftc_size_node_reset,
ftc_face_node_init): Check for errors before accepting a change.
* src/cache/ftcmru.c (FTC_MruList_New): Do nothing if reset fails.
2 files changed