don't limit the near plane to ~1mm (#1778)
don't limit the near plane to ~1mm (#1778)

We were not checking Camera's preconditions properly -- we assumed that
near < 1/1024 meant "near == 0".

Now we check preconditions properly and revert to the same hardcoded
default if they're not met -- doesn't matter what the default is,
it's there only to avoid NaNs and Infs elsewhere -- rendering will
be bogus eitherway.

Fixes #1766
google/filament,google/filament,google/filament,google/filament,google/filament,google/filament,google/filament,google/filament,google/filament,google/filament,google/filament,google/filament