Single variant single trait runs fail to generate QQplot

[roskamsh]

Upon running the targene-pipeline (v0.11.0) using a single variant and single trait, the final step GenerateOutputs() fails. Upon further inspection, this only occurs when the number of non-NA P-values per-estimator is 1. This would occur when you are running TarGene with only a single variant and single trait (currently experiencing this when reproducing FTO variant on BMI results on the AoU cohort).

Suggested changes:

• Make QQplot generation optional when only a single p-value (per-estimator) is present.
• Update targene-pipeline to make this output QQplot.png optional.

[olivierlabayle]

What is the reason behind the NA in this case?