PHALCON_INIT_NVAR(_PNULL) optimization
(cherry picked from commit ca8348dae904a0cec5cd14918bdbf4a3b99a5e5b)

Conflicts:
	ext/kernel/memory.c
Fix #1190
(cherry picked from commit 8d07edfbbe73880b21c46e6e738c7854d58fff0e)