Or HaChaim on Genesis 50:1/אור החיים על בראשית נ׳:א׳

1 וישק לו, he kissed him. The emphasis in this verse is on the word לו. Joseph kissed "him;" had Jacob been dead it would have been forbidden to kiss him seeing that the corpse exudes ritual impurity, and that impurity rises up to heaven and would harm the person who does the kissing. Inasmuch as Jacob had not died, however, Joseph was able to kiss him; Jacob simply appeared to be in a coma.