WORLDEDIT-3148 - Reported by SupaHam

[18:25:41 WARN]: Caused by: java.lang.IllegalArgumentException: density must be >= 1
[18:25:41 WARN]: at com.google.common.base.Preconditions.checkArgument(Preconditions.java:88)
[18:25:41 WARN]: at com.sk89q.worldedit.function.mask.NoiseFilter2D.setDensity(NoiseFilter2D.java:83)
[18:25:41 WARN]: at com.sk89q.worldedit.function.mask.NoiseFilter2D.(NoiseFilter2D.java:45)
[18:25:41 WARN]: at com.sk89q.worldedit.command.RegionCommands.flora(RegionCommands.java:477)