layers: Fix android build of safe_struct wrappers

Handle default case in switch statement for descriptor types.
diff --git a/vk_helper.py b/vk_helper.py
index 15c7ac7..87140ef 100755
--- a/vk_helper.py
+++ b/vk_helper.py
@@ -1664,6 +1664,8 @@
                                     '            }\n'
                                     '        }\n'
                                     '        break;\n'
+                                    '        default:\n'
+                                    '        break;\n'
                                     '    }\n'}
             for m in self.struct_dict[s]:
                 m_name = self.struct_dict[s][m]['name']