`cam` should give feedback when not entering because of invalid gamemode

[altrisi]

For example, if you're in creative cam doesn't take you to camera mode, but it also doesn't give you any feedback at all, which can be confusing.

I think it should either complain about wrong gamemode or, like the old java implementation, switch to spectator anyway.

[Ghoulboy78]

But if it switches you to spectator anyways, it will switch you back to survival when you switch back, unless we store takeoff gamemode too. I think it makes more sense to not allow to use command in creative mode, cos you can just do F4 + F3 to switch gamemode, or F3 + N.

What do you think?