BUG: Fix quantile calculation. Revert changes after merging master. #33200

Author: mabelvj

pandas/_libs/groupby.pyx

@@ -777,11 +777,8 @@ def group_quantile(ndarray[float64_t] out,
             counts[lab] += 1
             if not mask[i]:
                 non_na_counts[lab] += 1
-
-    if labels.any():
-        # Put '-1' (NaN) labels as the last group so it does not interfere
-        # with the calculations.
-        labels[labels==-1] = np.max(labels) + 1
+    # Put '-1' (NaN) labels as the last group so it does not interfere with the calculations.
+    labels[labels==-1] = np.max(labels) + 1
     # Get an index of values sorted by labels and then values
     order = (values, labels)
     sort_arr = np.lexsort(order).astype(np.int64, copy=False)