Fix pure cpp1 header file generated using -import-std

[MatthieuHernandez]

I've noticed that if I execute cppfront.exe with the -import-std option on a .h file that doesn't contain any cpp2 code, then an #endif will be missing at the end of the file. See #1320 for more info.

⚠️ I haven't added any test because I didn't see any tests with .h files.

[gregmarr]

A source without Cpp2 should be pass-through
(i.e., the Cpp2 source and the generated Cpp1 source should compare equal).

Unless you specify the flag to either import or include the standard library, then it adds extra stuff.

cppfront/source/to_cpp1.h

Lines 1298 to 1305 in 68b716a

	// Only emit extra lines if we actually have Cpp2, because
	// we want Cpp1-only files to pass through with zero changes
	// (unless the user requested import/include of std)
	if (
	source.has_cpp2()
	|| flag_import_std
	|| flag_include_std
	)

[gregmarr]

(flag_import_std || flag_include_std) to match

cppfront/source/to_cpp1.h

Lines 1301 to 1305 in 68b716a

	if (
	source.has_cpp2()
	|| flag_import_std
	|| flag_include_std
	)

[MatthieuHernandez]

I force-pushed with your suggestion. Thanks 😊

[hsutter]

Thanks for your pull request! It looks like this may be your first contribution to cppfront. I've emailed you the Contributor License Agreement (CLA), and once it's completed I can look at your pull request. Thanks again for your contribution.