coretasks: fix bad WHO tracking stuck in loop

`who_reqs` used to track `WHO` requests to the server flipped
keys/values and was never getting cleared upon `RPL_ENDOFWHO`.
Eventually, this would lead to an endless loop while the bot tried to
get an unused "querytype" (`randint`) in order to track `WHO` replies.

Now, key/values are in a more useful order (channel --map--> querytype).
Also, the unneccessary loop used to ensure unique values for the query type was
removed. A `RPL_WHOREPLY` includes the channel name in the response, so
confirming that the querytype for a channel matched is sufficient. The same
querytype could even be used for every channel without issue.

sopel/coretasks.py

@@ -702,9 +702,7 @@ def _send_who(bot, channel):
         # to identify the reply as one from this command, because if someone
         # else sent it, we have no fucking way to know what the format is.
         rand = str(randint(0, 999))
-        while rand in who_reqs:
-            rand = str(randint(0, 999))
-        who_reqs[rand] = channel
+        who_reqs[channel] = rand
         bot.write(['WHO', channel, 'a%nuachtf,' + rand])
     else:
         # We might be on an old network, but we still care about keeping our
@@ -1243,7 +1241,7 @@ def account_notify(bot, trigger):
 @plugin.priority('medium')
 def recv_whox(bot, trigger):
     """Track ``WHO`` responses when ``WHOX`` is enabled."""
-    if len(trigger.args) < 2 or trigger.args[1] not in who_reqs:
+    if len(trigger.args) < 2 or who_reqs.get(trigger.args[2]) is None:
         # Ignored, some plugin probably called WHO
         return
     if len(trigger.args) != 8:
@@ -1314,7 +1312,9 @@ def recv_who(bot, trigger):
 def end_who(bot, trigger):
     """Handle the end of a response to a ``WHO`` command (if needed)."""
     if 'WHOX' in bot.isupport:
-        who_reqs.pop(trigger.args[1], None)
+        stored_querytype = who_reqs.pop(trigger.args[1], None)
+        if stored_querytype is None:
+            LOGGER.debug("Attempted to handle an untracked WHO reply for '%s'", trigger.args[1])
 
 
 @module.event('AWAY')