Fails to build with GCC 16

[sergiodj]

Hi there,

cJSON fails to build with GCC 16 on GNU/Linux:

In file included from /home/build/tests/unity/src/unity.h:16,
                 from /home/build/tests/misc_tests.c:28:
/home/build/tests/misc_tests.c: In function 'cjson_set_valuestring_should_return_null_if_strings_overlap':
/home/build/tests/misc_tests.c:504:22: error: 'strcmp' reading 1 or more bytes from a region of size 0 [-Werror=stringop-overread]
  504 |     TEST_ASSERT_TRUE(strcmp(str, "bcde") == 0);
      |                      ^~~~~~~~~~~~~~~~~~~
/home/build/tests/unity/src/unity_internals.h:652:102: note: in definition of macro 'UNITY_TEST_ASSERT'
  652 | #define UNITY_TEST_ASSERT(condition, line, message)                                              if (condition) {} else {UNITY_TEST_FAIL((UNITY_LINE_TYPE)(line), (message));}
      |                                                                                                      ^~~~~~~~~
/home/build/tests/misc_tests.c:504:5: note: in expansion of macro 'TEST_ASSERT_TRUE'
  504 |     TEST_ASSERT_TRUE(strcmp(str, "bcde") == 0);
      |     ^~~~~~~~~~~~~~~~
cc1: note: source object is likely at address zero
cc1: all warnings being treated as errors