if the weighted sum of scores is 0, they are more likely all nans and…

… we shouldn't report an overall score. h/t @mcguirepatr

src/ILAMB/Confrontation.py

@@ -705,6 +705,8 @@ def _computeOverallScore(scalars):
                         weight = self.weight[score]
                     overall_score += weight * scalars.variables[v][...]
                     sum_of_weights += weight
+                if np.abs(overall_score) < 1e-12:
+                    overall_score = np.nan
                 overall_score /= max(sum_of_weights, 1e-12)
                 scores["Overall Score %s" % region] = overall_score
             return scores