sepolicy: don't construct mappings for ignored types

Say, foo_type was introduced in 29.0 sepolicy and is in 29.0.ignore.cil.
Also assume (typeattributeset foo_type_29_0 (foo_type bar_type))

Make sure that above mapping is not expanded into 28.0.cil, 27.0.cil, etc.

Test: m selinux_policy
Test: build aosp/1199739
Change-Id: Ib564431ab67f555ea1ae650dc31a68121e9c6d84

tests/combine_maps.py

@@ -45,6 +45,11 @@ def Combine(top, bottom):
         # Typeattributes in V.v.cil have _V_v suffix, but not in V.v.ignore.cil
         bottom_type = m.group(1) if m else top_ta
 
+        # If type doesn't exist in bottom map, no need to maintain mappings to
+        # that type.
+        if bottom_type not in bottom.rTypeattributesets.keys():
+            continue
+
         for bottom_ta in bottom.rTypeattributesets[bottom_type]:
             bottom.typeattributesets[bottom_ta].update(top_type_set)