libcuse: Fix memory leak in cuse_init()

[zlei]

Summary

The mutex attributes object should be destroyed after been used.

Where here also check return value of pthread_mutexattr_init() to
prevent potential writing in unallocated memory or NULL pointer
dereferencing when the system is out of memory.

This fix is inspired by the recent commit a03f768612ad
(libstdthreads: destroy mutexattr in mtx_init()) .

MFC after: 1 week

[zlei]

lib/libcuse/cuse_lib.c

113

Emm, return value of pthread_mutex_init() is not checked ;(