Make sure its defined

Signed-off-by: Adam Li <adam2392@gmail.com>

Author: adam2392

sklearn/tree/_splitter.pyx

@@ -959,6 +959,13 @@ cdef inline int node_split_random(
             current_split.threshold
         )
 
+        if missing_go_to_left:
+            n_left = current_split.pos - start + n_missing
+            n_right = end_non_missing - current_split.pos
+        else:
+            n_left = current_split.pos - start
+            n_right = end_non_missing - current_split.pos + n_missing
+
         # Reject if min_samples_leaf is not guaranteed
         if splitter.check_presplit_conditions(&current_split, n_missing, missing_go_to_left) == 1:
             continue