fix: nil-guard GetChannelName, GetGuildRosterInfo, InterfaceOptions* on CoA client

PlayerNames.lua:94 - GetChannelName can return nil on the CoA-Beta client
when the active channel target is not joined; capture into a local and
fall back to empty string instead of chaining :lower() on nil.

PlayerNames.lua:344 - GetGuildRosterInfo(i) returns nil name/class on
this client (same family as the AltNames.lua fix in 1c4a7e8). Skip the
iteration when name is nil to avoid indexing channels.GUILD[nil] and
passing nil into AddPlayer.

Chatter.lua:204 OpenConfig and Chatter.lua:21 inline func - the Blizzard
InterfaceOptionsFrame globals are absent on CoA-Beta, so calling
IsResizable() or InterfaceOptionsFrame_OpenToCategory() throws. Guard
both call sites and fall back to opening the standalone AceConfigDialog
window.

ChatScroll.lua:53 - InterfaceOptionsSocialPanelChatMouseScroll_SetScrolling
is also missing on this client; only hook it when the global exists,
otherwise AceHook errors out at OnInitialize.

Modules/ChatScroll.lua

@@ -50,7 +50,9 @@ local options = {
 function mod:OnInitialize()
 	self.db = Chatter.db:RegisterNamespace(self:GetName(), defaults)
 	self:RegisterEvent("CVAR_UPDATE", "ChangedVars")
-	self:RawHook("InterfaceOptionsSocialPanelChatMouseScroll_SetScrolling",true)
+	if _G.InterfaceOptionsSocialPanelChatMouseScroll_SetScrolling then
+		self:RawHook("InterfaceOptionsSocialPanelChatMouseScroll_SetScrolling",true)
+	end
 end
 
 function mod:InterfaceOptionsSocialPanelChatMouseScroll_SetScrolling()