Khan is deliberately stressing the word "IF" as he acknowledges the possibility that there may be some problem,
and then positively confirming he would not hesitate in "calling it out" .. IF and WHEN he might ever encounter it...

He DOES call it out, and he accuses Corbyn of "failing to call it out."
That was in the Indy headline and the text,
"Jeremy Corbyn accused of failing to 'call out' Labour antisemitism by Sadiq Khan."