Array bounds check missing for zero length string in REMOVE_TRAILING_SLASHES

[bojake]

While minor, sending "" into the REMOVE_TRAILING_SLASHES macro will result in a buffer underflow read because of the while that does not have a bounds check.

REMOVE_TRAILING_SLASHES(""):

do {
size_t _len = strlen(""); // _len = 0
while (_str[_len-1] == '/') { _str[--_len] = '\0'; } // while(_str[-1] == '/') { _str[-1] = '\0'; }
} while(0);

also is true if you give it "/" or "///" or "////////////////////////////////////////", you get it.

Change the while to be

while(_len>0 && _str[_len-1] == '/')