Fix case with empty GT

Closes #309 (closed)

dan/ocr/manager/metrics.py

@@ -207,7 +207,7 @@ class MetricManager:
                     metrics[keyword + "_error_rate" + suffix] = [
                         round(float(edit_dist / gt_len), 4)
                         if gt_len != 0
-                        else float(edit_dist == 0)
+                        else float(edit_dist != 0)
                         for edit_dist, gt_len in zip(
                             metrics["edit_" + keyword + suffix],
                             metrics["nb_" + keyword + suffix],