Description:
------------
a pointer isn't checked within zend_extension.c which can cause segfaults

i had the problem using current version of DBG extension no as zend_extension installed

but the cause of this is a not validated pointer

i checked actual php5.2 CSV and the bug can also be found there on line 221 of file Zend/zend_extension.c
---------------------------
zend_extension *extension = (zend_extension *) element->data;
if (!strcmp(extension->name, extension_name)) {
	return extension;
}
---------------------------
extension isn't checked if it is NULL and strcmp doesn't care
extension_name was correct as seen in the backtrace

Reproduce code:
---------------
host:/home/testuser # php5 -r 'print "BUGG";'
BUGGSegmentation fault
host:/home/testuser #


Expected result:
----------------
host:/home/testuser # php5 -r 'print "BUGG";'
BUGG
host:/home/testuser #

Actual result:
--------------
(gdb) run -r 'print "BUGG";'
Starting program: /usr/bin/php5 -r 'print "BUGG";'
[Thread debugging using libthread_db enabled]
[New Thread 182910915616 (LWP 20652)]
BUGG
Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 182910915616 (LWP 20652)]
0x0000002a963b73c3 in strcmp () from /lib64/tls/libc.so.6
(gdb) bt
#0  0x0000002a963b73c3 in strcmp () from /lib64/tls/libc.so.6
#1  0x000000000054cb96 in zend_get_extension (extension_name=0x2a9727629d "DBG") at /usr/src/debug/php-5.1.6/Zend/zend_extensions.c:221
#2  0x0000002a9726e50c in zm_shutdown_dbg (type=<value optimized out>, module_number=18) at /home/mcls/dbg-2.15.1/dbg.c:926
#3  0x0000000000548613 in module_destructor (module=0x7fe030) at /usr/src/debug/php-5.1.6/Zend/zend_API.c:1811
#4  0x000000000054dc86 in zend_hash_apply_deleter (ht=0x79ed20, p=0x7fdfd0) at /usr/src/debug/php-5.1.6/Zend/zend_hash.c:576
#5  0x000000000054de68 in zend_hash_graceful_reverse_destroy (ht=0x79ed20) at /usr/src/debug/php-5.1.6/Zend/zend_hash.c:642
#6  0x00000000005443d7 in zend_shutdown () at /usr/src/debug/php-5.1.6/Zend/zend.c:728
#7  0x000000000050699a in php_module_shutdown () at /usr/src/debug/php-5.1.6/main/main.c:1618
#8  0x00000000005b70d0 in main (argc=3, argv=0x7fbffff498) at /usr/src/debug/php-5.1.6/sapi/cli/php_cli.c:1252
(gdb)