Fix annoying deathReporter error

Modules/DeathReporter.lua

@@ -101,6 +101,7 @@ function shared.DeathReporter.Init()
 	systemMessageFrame:SetScript("OnEvent", function(self, event, msg)
 		if not Heimdall_Data.config.deathReporter.enabled then return end
 		local source, destination = string.match(msg, "([^ ]+) has defeated ([^ ]+) in a duel")
+		if not source or not destination then return end
 		source = string.match(source, "([^-]+)")
 		destination = string.match(destination, "([^-]+)")
 		if source and destination then