Only set player weather if a plugin requested it.

If the server changes the weather it will set the per-player weather
variable and future changes will not apply. We should only set this
variable when a plugin is requesting per-player weather and not when
the server it doing it.

src/main/java/net/minecraft/server/EntityPlayer.java

@@ -841,7 +841,10 @@ public class EntityPlayer extends EntityHuman implements ICrafting {
             return;
         }
 
+        if (plugin) {
             this.weather = type;
+        }
+
         this.playerConnection.sendPacket(new Packet70Bed(type == WeatherType.DOWNFALL ? 1 : 2, 0));
     }