Fixes runtimes caused by null client preferences (#16464)

* Client check

* Skip character randomisation

code/modules/client/preference/preferences_mysql.dm

@@ -126,10 +126,11 @@
 	qdel(query)
 	return 1
 
-/datum/preferences/proc/load_character(client/C,slot)
+/datum/preferences/proc/load_character(client/C, slot)
 	saved = FALSE
 
-	if(!slot)	slot = default_slot
+	if(!slot)
+		slot = default_slot
 	slot = sanitize_integer(slot, 1, max_save_slots, initial(default_slot))
 	if(slot != default_slot)
 		default_slot = slot
@@ -142,6 +143,10 @@
 			return
 		qdel(firstquery)
 
+	if(!C) // If the client disconnected during the query, try again later.
+		qdel(src)
+		return TRUE
+
 	// Let's not have this explode if you sneeze on the DB
 	var/datum/db_query/query = SSdbcore.NewQuery({"SELECT
 					OOC_Notes,