fix uptime for uptime of less than a second (#3009)

* fix uptime for uptime of less than a second

* changelog

* More conclusive fix

redbot/core/global_checks.py

@@ -3,11 +3,19 @@ from . import commands
 
 
 def init_global_checks(bot):
+    @bot.check_once
+    def actually_up(ctx):
+        """ 
+        Uptime is set during the initial startup process.
+        If this hasn't been set, we should assume the bot isn't ready yet. 
+        """
+        return ctx.bot.uptime is not None
+
     @bot.check_once
     async def whiteblacklist_checks(ctx):
         return await ctx.bot.allowed_by_whitelist_blacklist(ctx.author)
 
     @bot.check_once
-    async def bots(ctx):
+    def bots(ctx):
         """Check the user is not another bot."""
         return not ctx.author.bot