Fixes spawning with psionics. (#16969)

Fixes a error when sanitizing a character that doesnt have psionics.
Fixes #16966

Co-authored-by: Werner <Arrow768@users.noreply.github.com>

code/modules/client/preference_setup/general/07_psionics.dm

@@ -49,6 +49,9 @@
 	)
 
 /datum/category_item/player_setup_item/general/psionics/load_special(savefile/S)
+	if(!pref.psionics)
+		pref.psionics = "{}"
+
 	var/before = pref.psionics
 	try
 		pref.psionics = json_decode(pref.psionics)