wil6210: check null pointer in _wil_cfg80211_merge_extra_ies

ies1 or ies2 might be null when code inside
_wil_cfg80211_merge_extra_ies access them.
Add explicit check for null and make sure ies1/ies2 are not
accessed in such a case.

spos might be null and be accessed inside
_wil_cfg80211_merge_extra_ies.
Add explicit check for null in the while condition statement
and make sure spos is not accessed in such a case.

Signed-off-by: Alexei Avshalom Lazar <ailizaro@codeaurora.org>
Signed-off-by: Maya Erez <merez@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>