BUG/MEDIUM: stats: Require more room if buffer is almost full

This was lost with commit f4258bdf3 ("MINOR: stats: Use the applet API to
write data"). When the buffer is almost full, the stats applet gives up.
When this happens, the applet must require more room. Otherwise, data in the
channel buffer are sent to the client but the applet is not woken up in
return.

It is a 2.8-specific bug, no backport needed.
1 file changed