Allow empty bounds in Camera::ResetToBounds

Although it is generally wrong to try to call `ResetToBounds` with a
`Bounds` object that does not have a valid range, there are cases where
the range might not be valid. (For example, if `ResetToBounds` was
called in a routine that is rendering an empty scene, it would be best
not to crash.)
6 jobs for reset-bounds-empty in 0 seconds
Status Name Job ID Coverage
  External
passed cdash-buildbot

passed vtk-m-dragnipur-osx-shared-debug+32bit_ids+64bit_coords+clang+tbb

00:09:30

passed vtk-m-dragnipur-osx-static-release+64bit_coords+clang+tbb

00:00:18

passed vtk-m-osheim-windows-shared-debug+ninja-vs-2017+tbb

00:21:12

failed vtk-m-osheim-windows-static-release+ninja-vs-2017+tbb

00:12:36

passed cdash-buildbot