util.termwidth: a file-like object may legitimately lack a fileno() method

Spotted in the wild when running a hook while pushing over HTTPS.

mercurial/util.py

@@ -1438,7 +1438,10 b' def termwidth():'
         import termios, array, fcntl
         for dev in (sys.stdout, sys.stdin):
             try:
-                fd = dev.fileno()
+                try:
+                    fd = dev.fileno()
+                except AttributeError:
+                    continue
                 if not os.isatty(fd):
                     continue
                 arri = fcntl.ioctl(fd, termios.TIOCGWINSZ, '\0' * 8)