Add a check in cJSON_Minify

[lxyjy6]

The char* json in cJSON_Minify may not end with '\0', so I've added an extra condition in the while loop.

[imaami]

This does not prevent what it purports to fix. strlen() relies on the string having a null terminator. It scans for a null byte and reports the length based on it. If the input string isn't terminated, strlen() will read past the end of the buffer just like the current code would.