[BUG] Invalid memory read in zim_Phalcon_Cache_Backend_Memcache_flush

[ghost]

See https://travis-ci.org/sjinks/cphalcon/jobs/13227018#L320

==14731== Invalid read of size 8
==14731== at 0x835D23: zend_hash_move_forward_ex (/tmp/php-build/source/5.4.16/Zend/zend_hash.c:1126)
==14731== by 0xF179D14: zim_Phalcon_Cache_Backend_Memcache_flush (/home/travis/build/sjinks/cphalcon/ext/cache/backend/memcache.c:617)
==14731== by 0xEFFF377: phalcon_execute_internal (/home/travis/build/sjinks/cphalcon/ext/phalcon.c:385)
==14731== by 0x8DB461: zend_do_fcall_common_helper_SPEC (/tmp/php-build/source/5.4.16/Zend/zend_vm_execute.h:645)
==14731== by 0x88FA3C: execute (/tmp/php-build/source/5.4.16/Zend/zend_vm_execute.h:410)
==14731== by 0x817D3E: zend_call_function (/tmp/php-build/source/5.4.16/Zend/zend_execute_API.c:958)
==14731== by 0x677919: zim_reflection_method_invokeArgs (/tmp/php-build/source/5.4.16/ext/reflection/php_reflection.c:3018)
==14731== by 0xEFFF377: phalcon_execute_internal (/home/travis/build/sjinks/cphalcon/ext/phalcon.c:385)
==14731== by 0x8DB461: zend_do_fcall_common_helper_SPEC (/tmp/php-build/source/5.4.16/Zend/zend_vm_execute.h:645)
==14731== by 0x88FA3C: execute (/tmp/php-build/source/5.4.16/Zend/zend_vm_execute.h:410)
==14731== by 0x827C0B: zend_execute_scripts (/tmp/php-build/source/5.4.16/Zend/zend.c:1315)
==14731== by 0x7BB008: php_execute_script (/tmp/php-build/source/5.4.16/main/main.c:2494)
==14731== Address 0x12d35400 is 32 bytes inside a block of size 77 free'd
==14731== at 0x4C2A82E: free (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==14731== by 0x834B43: zend_hash_del_key_or_index (/tmp/php-build/source/5.4.16/Zend/zend_hash.c:536)
==14731== by 0xF008D21: phalcon_array_unset (/home/travis/.phpenv/versions/5.4.16/include/php/Zend/zend_hash.h:358)
==14731== by 0xF179CA5: zim_Phalcon_Cache_Backend_Memcache_flush (/home/travis/build/sjinks/cphalcon/ext/cache/backend/memcache.c:624)
==14731== by 0xEFFF377: phalcon_execute_internal (/home/travis/build/sjinks/cphalcon/ext/phalcon.c:385)
==14731== by 0x8DB461: zend_do_fcall_common_helper_SPEC (/tmp/php-build/source/5.4.16/Zend/zend_vm_execute.h:645)
==14731== by 0x88FA3C: execute (/tmp/php-build/source/5.4.16/Zend/zend_vm_execute.h:410)
==14731== by 0x817D3E: zend_call_function (/tmp/php-build/source/5.4.16/Zend/zend_execute_API.c:958)
==14731== by 0x677919: zim_reflection_method_invokeArgs (/tmp/php-build/source/5.4.16/ext/reflection/php_reflection.c:3018)
==14731== by 0xEFFF377: phalcon_execute_internal (/home/travis/build/sjinks/cphalcon/ext/phalcon.c:385)
==14731== by 0x8DB461: zend_do_fcall_common_helper_SPEC (/tmp/php-build/source/5.4.16/Zend/zend_vm_execute.h:645)
==14731== by 0x88FA3C: execute (/tmp/php-build/source/5.4.16/Zend/zend_vm_execute.h:410)
==14731==