WORLDGUARD-3492 - Reported by Byteflux

Tried setting up a region on my server's spawn where players can be automatically fed, but when it didn't work I found that the flag is ignored when the player is determined to be invincible.

Upon further digging I found these relevant snippets from the source:
https://github.com/sk89q/WorldGuard/blob/master/src/main/java/com/sk89q/worldguard/session/handler/FeedFlag.java#L38
https://github.com/sk89q/WorldGuard/blob/master/src/main/java/com/sk89q/worldguard/session/handler/HealFlag.java#L41