Extract code to choose among matched lines while loading UL.

This commit refs #12803

load.py

@@ -459,18 +459,11 @@ class LoadOrder(metaclass=PoolMeta):
                     matched_lines = lines
 
             # check overload line qty
-            line = None
-            for _line in matched_lines:
-                order_lines.setdefault(_line.id,
-                    _line.ul_quantity - len(_line.unit_loads))
-                if order_lines[_line.id] > 0:
-                    line = _line
-                    break
+            line = self._choose_matched_line(matched_lines, order_lines,
+                unit_load)
             if line:
-                order_lines[line.id] -= 1
-
                 # load UL
-                unit_load.load_line = _line
+                unit_load.load_line = line
             elif unit_load not in failed_uls:
                 self.raise_user_error('ul_overload', self.rec_name)
 
@@ -480,6 +473,19 @@ class LoadOrder(metaclass=PoolMeta):
 
         UL.save(unit_loads)
 
+    def _choose_matched_line(self, lines, values, unit_load):
+        line = None
+        for _line in lines:
+            if _line.id not in values:
+                values.setdefault(_line.id, set(
+                    ul for ul in _line.unit_loads))
+            if _line.ul_quantity - len(values[_line.id]) > 0:
+                line = _line
+                break
+        if line:
+            values[line.id].add(unit_load)
+        return line
+
     def check_origin_restrict(self, unit_load, origin_restrict,
             origin_restrict_warn):
         lines = []