Zero LAI/SAI/RAI yields nonzero respiration

[kmdeck]

Describe the bug

In the "no plant" testset from test/standalone/Vegetation/plant_hydraulics.jl, I noticed we have nonzero Ra. I believe it is because within this function: https://github.com/CliMA/ClimaLSM.jl/blob/982bd55d8629b792e5852667cc2e18b5502b0dda/src/standalone/Vegetation/autotrophic_respiration.jl#L69 (which needs a doc string :) ), we first get all zeros: https://github.com/CliMA/ClimaLSM.jl/blob/982bd55d8629b792e5852667cc2e18b5502b0dda/src/standalone/Vegetation/autotrophic_respiration.jl#L82 but then nonzero: https://github.com/CliMA/ClimaLSM.jl/blob/982bd55d8629b792e5852667cc2e18b5502b0dda/src/standalone/Vegetation/autotrophic_respiration.jl#L83-L84

Either beta or Rd must be zero to get zero back here: https://github.com/CliMA/ClimaLSM.jl/blob/982bd55d8629b792e5852667cc2e18b5502b0dda/src/standalone/Vegetation/canopy_parameterizations.jl#L902, but neither is.

Not sure about this: GPP is zero, so we get a negative number: https://github.com/CliMA/ClimaLSM.jl/blob/982bd55d8629b792e5852667cc2e18b5502b0dda/src/standalone/Vegetation/canopy_parameterizations.jl#L921