CVE-2026-103022: Urwid: handle_short_request() crashes on non-ASCII POST body (UnicodeEncodeError DoS)

The handle_short_request() function in urwid/display/web.py raises an unhandled UnicodeEncodeError when processing a POST request body containing non-ASCII bytes. The function reads POST input and encodes it to ASCII before writing to a named pipe. Any byte value above 0x7F causes the CGI process to exit with an unhandled exception, returning an HTTP 500 error to the client. Additionally, a file descriptor opened earlier in the same function is not closed before the exception propagates, causing a file descriptor leak for the lifetime of the CGI process.

A second instance of missing exception handling exists in the polling update path, where non-UTF-8 socket output causes an unhandled UnicodeDecodeError.