Process crash via trailing backslash in awk regex

A heap-buffer overflow in BusyBox awk 1.36.1 allows local users to crash the process with a crafted awk program file. In next_token, a trailing backslash in an invalid regular expression leaves the escape pointer unchanged, causing the parser to advance past the terminating NUL and read beyond the heap allocation. Reachability requires a user or process to invoke BusyBox awk on the malformed file; the demonstrated consequence is a process abort, with no published write primitive.