#4298 Handle various out of memory cases

[akleshchev]

1. Fast timers were moved out of debug long time ago, yet debug was still initializing them without need (arguably it doesn't need to init everything else too). And we got an out of memory crash there. Free those resources.
2. LLSDSerialize::fromBinary seems to be a genuine out of memory, but just in case of botched cache, cleared that.
3. Just slightly smarter logging for inventory
4. Font loading crashes out of memory. Nothing we can do that but properly log and report it (to both user and statistics).