Add can_produce_data() method to AdjustedAlgorithm

AdjustedAlgorithm.process() essentially adjusts two values:

 - 3D vector field HEZ_raw -> XYZ_adj
 - 1D scalar field F_raw -> F_adj

Neither should depend on the other, but this was implicitly the case
as originally implemented. When F was missing, this prevented XYZ
from being calculated, at least when called in 'update' mode by the
Controller. Likewise, if HEZ were missing, this prevented adjusted F
from being calculated.