gallium: Pass 512 bytes max to EngDebugPrint.

src/gallium/auxiliary/util/p_debug.c

@@ -76,7 +76,7 @@ void _debug_vprintf(const char *format, va_list ap)
    /* EngDebugPrint does not handle float point arguments, so we need to use
     * our own vsnprintf implementation. It is also very slow, so buffer until
     * we find a newline. */
-   static char buf[512 + 1] = {'\0'};
+   static char buf[512] = {'\0'};
    size_t len = strlen(buf);
    int ret = util_vsnprintf(buf + len, sizeof(buf) - len, format, ap);
    if(ret > (int)(sizeof(buf) - len - 1) || util_strchr(buf + len, '\n')) {