cmd: lwip/wget: avoid NULL dereference in _set_cacert()

cmd: lwip/wget: avoid NULL dereference in _set_cacert()

Running `wget cacert builtin` leads to a crash in _set_cacert():

    Unhandled exception: Load access fault

Function _set_cacert() dereferences variable wget_info.
We must initialize it before executing the cacert sub-command.

Fixes: d3761a31ef09 ("lwip: split net/lwip/wget.c")
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Jerome Forissier <jerome.forissier@linaro.org>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>