scripts: Remove asserts from struct size helpers

Unknown structures will return a 0 size instead of failing, in order for
them to be ignored properly.
diff --git a/scripts/helper_file_generator.py b/scripts/helper_file_generator.py
index 84b8c7b..3d4ef46 100644
--- a/scripts/helper_file_generator.py
+++ b/scripts/helper_file_generator.py
@@ -447,8 +447,8 @@
     # Build the footer of the get_struct_chain_size function
     def GenerateChainSizePostamble(self):
         postamble  = '            default:\n'
-        postamble += '                assert(0);\n'
         postamble += '                struct_size += 0;\n'
+        postamble += '                break;'
         postamble += '        }\n'
         postamble += '        pNext = (VkApplicationInfo*)pNext->pNext;\n'
         postamble += '    }\n'
@@ -465,7 +465,6 @@
     # Build the footer of the get_struct_size function
     def GenerateStructSizePostamble(self):
         postamble  = '    default:\n'
-        postamble += '        assert(0);\n'
         postamble += '        return(0);\n'
         postamble += '    }\n'
         postamble += '}'