Fix plain username lookup for Guild.get_member_named

Fix #9451

discord/ext/commands/converter.py

@@ -207,6 +207,11 @@ class MemberConverter(IDConverter[discord.Member]):
     async def query_member_named(self, guild: discord.Guild, argument: str) -> Optional[discord.Member]:
         cache = guild._state.member_cache_flags.joined
         username, _, discriminator = argument.rpartition('#')
+
+        # If # isn't found then "discriminator" actually has the username
+        if not username:
+            discriminator, username = username, discriminator
+
         if discriminator == '0' or (len(discriminator) == 4 and discriminator.isdigit()):
             lookup = username
             predicate = lambda m: m.name == username and m.discriminator == discriminator
@@ -316,6 +321,11 @@ async def convert(self, ctx: Context[BotT], argument: str) -> discord.User:
             return result  # type: ignore
 
         username, _, discriminator = argument.rpartition('#')
+
+        # If # isn't found then "discriminator" actually has the username
+        if not username:
+            discriminator, username = username, discriminator
+
         if discriminator == '0' or (len(discriminator) == 4 and discriminator.isdigit()):
             predicate = lambda u: u.name == username and u.discriminator == discriminator
         else:

discord/guild.py

@@ -1104,6 +1104,11 @@ def get_member_named(self, name: str, /) -> Optional[Member]:
         members = self.members
 
         username, _, discriminator = name.rpartition('#')
+
+        # If # isn't found then "discriminator" actually has the username
+        if not username:
+            discriminator, username = username, discriminator
+
         if discriminator == '0' or (len(discriminator) == 4 and discriminator.isdigit()):
             return utils.find(lambda m: m.name == username and m.discriminator == discriminator, members)