[BUG] filters blockcount and blockcountlessthan can't be used together.

[FoxWyvern]

Using the filters blockcount and blockcountlessthan together kicks back the following error:

2015-06-26 21:13:52.0380|Info|ChatHandler Error: System.ArgumentException: An it
em with the same key has already been added.
at System.Collections.Generic.Dictionary`2.Insert(TKey key, TValue value, Boo
lean add)
at EssentialsPlugin.Utility.CubeGrids.ScanGrids(UInt64 userId, String[] words
)
at EssentialsPlugin.ChatHandlers.AdminScan.HandleAdminScanGrids.HandleCommand
(UInt64 userId, String[] words)
at EssentialsPlugin.Essentials.HandleChatMessage(UInt64 steamId, String messa
ge)

Examples of commands used:
/admin scan grids "hascustomname:Military Escort" blockcount:223 blockcountlessthan:224 includesblocksubtype:beacon blocksize:largeship
/admin scan grids "hascustomname:Private Sail" blockcountlessthan:79 blockcount:78 includesblocksubtype:beacon blocksize:largeship
/admin scan grids "hascustomname:Business Shipment" blockcountlessthan:148 blockcount:147 includesblocksubtype:beacon blocksize:largeship
/admin scan grids "hascustomname:Mining Carriage" blockcountlessthan:193 blockcount:192 includesblocksubtype:beacon blocksize:largeship
/admin scan grids "hascustomname:Commercial Freighter" blockcountlessthan:484 blockcount:483 includesblocksubtype:beacon blocksize:largeship
/admin scan grids "hascustomname:Mining Transport" blockcountlessthan:252 blockcount:251 includesblocksubtype:beacon blocksize:largeship
/admin scan grids "hascustomname:Mining Hauler" blockcountlessthan:1484 blockcount:1483 includesblocksubtype:beacon blocksize:largeship
/admin scan grids "hascustomname:Military Minelayer" blockcountlessthan:674 blockcount:673 includesblocksubtype:beacon blocksize:largeship
/admin scan grids "hascustomname:Military Transporter" blockcountlessthan:2712 blockcount:2711 includesblocksubtype:beacon blocksize:largeship