net: zero terminate string with headers in wget_fill_info()

net: zero terminate string with headers in wget_fill_info()

Commit 2dd076a9c1b4 ("net: wget: integrate struct wget_info into legacy
wget code") introduced function wget_fill_info() which retrieves the
headers from the HTTP server response. As we want to parse the string in
later patches we need to ensure that it is NUL terminated.

We must further check that wget_info->headers in not NULL.
Otherwise a crash occurs.

Fixes: 2dd076a9c1b4 ("net: wget: integrate struct wget_info into legacy wget code")
Signed-off-by: Adriano Cordova <adrianox@gmail.com>
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>