munit_assert_string_equal on two null pointers provoque SEGFAULT

[crazyhouse33]

Hi, I just cloned master from this repo and used you code on my debian machine.

Hi, take a look at that gdb session that illustrate the problem:

11			munit_assert_string_equal(argc[i], expected[i]);
2: argc[i] = 0x0
3: expected[i] = 0x0
(gdb) n

Program received signal SIGSEGV, Segmentation fault.
__strcmp_sse2_unaligned ()
    at ../sysdeps/x86_64/multiarch/strcmp-sse2-unaligned.S:31
31	../sysdeps/x86_64/multiarch/strcmp-sse2-unaligned.S: Aucun fichier ou dossier de ce type.

I understand the bug but I feel that it maybe a good idea to add a check that checks for the NULL == NULL(actually checking that two pointers are equals should be stronger and include more use cases) case on your asserts since a lot of function return NULL when they should return whatever the pointer to indicate a fail. And for automation testing sometimes by using your asserts on my expected result list I ran into the problem twice already. I don't see drawbacks of checking the case but you are more suited to think about what could go wrong. It would save some testcase re-arranging. Thanks for your work tho.