fix: validate values that could cause divide by 0

[hellkite500]

Closes #52 by validating several config and/or forcing values which could lead to divide by zero situations.

Changes

• Prints to stderr and exists in most cases, but a default small wind_speed is used with a warning printed instead of a hard stop.

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[aaraney]

One comment to look at but i'll go ahead and approve this. Thanks, @hellkite500!

[ajkhattak]

I think this needs to be removed. If we look at

zm=wind_speed_measurement_height_m;   // is set to 2 m
zh=humidity_measurement_height_m;     // is set to 2 m
d= zero_plane_displacement_height_m;   // = d = 2/3 * veg_height

 Technically, d can be greater than 2.0 for most of the case, if that happens, it is reset based on zh (below)
 
  if (d >= zh) {
    d = 2.0/3.0 * zh;
  }
  
so (zm-d) will always be positive, and so is (zh-d) in the log terms of Ra

let's talk about it if you believe I am missing something

[hellkite500]

I have relaxed the strict displacement and measurement height checks, and instead implemented the assumption that when displacement height > measurement height then the measured wind speed is just used as the 2M wind speed, since in this case the log profile isn't valid.

This check also would have caused a failure that was indirectly accounted for in at least one method where humidity measurement height was used to compute a new displacement and transform, so the aerodynamic resistance computation now ensures valid numerical conditions, and the aorc forcing model param is validated to have a humidity measurement height of 2 meters.