Adjust plotDiet() to Restrict Plots to Relevant Size Ranges

[JamesRimmerEco]

When using the plotDiet() function, the diet plots currently extend all the way to w_max, regardless of whether there are any fish left at those sizes. This can make the plots misleading or less helpful for species with little or no biomass in the largest size classes, as they may show diet information for size ranges where the species is no longer present, extending to rare situations where diets would require negative intake rates for very large fish.

It might be helpful to adjust plotDiet() so that it only plots up to the largest size class where fish are present (i.e., where the abundance is greater than zero). This would ensure the plot better represents the relevant size ranges and provides more useful information to the user.

[gustavdelius]

Thanks @JamesRimmerEco . That would be a good idea. In practice, the abundance of fish actually stays non-zero all the way up to w_repro_max but the abundance can become totally negligibly small long before that. So the relevant size range should not be the entire range where the abundance is greater than 0 but only the range where it is greater than some threshold. The trick will be to automatically find a good value for this threshold.