wget: handle URLs with @ or hash differently

wget: handle URLs with @ or hash differently

If server replied with 302 and

Location: ?foo

we used to underflow the allocated space while trying to form the "@foo"
filename. Switch to forming "foo" filename.

function                                             old     new   delta
packed_usage                                       32795   32799      +4
parse_url                                            387     352     -35
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 1/1 up/down: 4/-35)             Total: -31 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>