Fixes #580. Checks if statistic is defined in collection before setting

value.  Defaults to 0, if statistic not found and logs message in case statistic
should exist (e.g. if schema changes and map/reduce function is incorrect).

packages/rocketchat-lib/server/functions/getStatistics.coffee

@@ -46,9 +46,24 @@ RocketChat.getStatistics = ->
 
 	result = ChatRoom.mapReduce(m, r, { finalize: f, out: "rocketchat_mr_statistics" })
 
-	statistics.maxRoomUsers = MapReducedStatistics.findOne({ _id: 1 }).value.max
-	statistics.avgChannelUsers = MapReducedStatistics.findOne({ _id: 'c' }).value.avg
-	statistics.avgPrivateGroupUsers = MapReducedStatistics.findOne({ _id: 'p' }).value.avg
+	statistics.maxRoomUsers = 0 
+	statistics.avgChannelUsers = 0
+	statistics.avgPrivateGroupUsers = 0
+
+	if MapReducedStatistics.findOne({ _id: 1 })
+		statistics.maxRoomUsers = MapReducedStatistics.findOne({ _id: 1 }).value.max
+	else 
+		console.log 'max room user statistic not found'.red
+
+	if MapReducedStatistics.findOne({ _id: 'c' })
+		statistics.avgChannelUsers = MapReducedStatistics.findOne({ _id: 'c' }).value.avg
+	else
+		console.log 'channel user statistic not found'.red
+
+	if MapReducedStatistics.findOne({ _id: 'p' })
+		statistics.avgPrivateGroupUsers = MapReducedStatistics.findOne({ _id: 'p' }).value.avg 
+	else
+		console.log 'private group user statistic not found'.red
 	
 	os = Npm.require('os')
 	statistics.os =