cpp_source fails to compile indented void-returning function

If a void-returning function marked with `cpp11::register` is indented, cpp11 fails to recognize the void return type and will try to use its result in the wrapper it generates. ```r # This works cpp11::cpp_source(code = "[[cpp11::register]]\nvoid foo() {}") # This fails to compile. Note the extra space character between the newline and void cpp11::cpp_source(code = "[[cpp11::register]]\n void foo() {}") ``` ``` using C++ compiler: ‘g++ (GCC) 14.2.1 20241116’ using C++11 /tmp/nix-shell.Cz8fPO/RtmpadKzBh/code_16bff7617b36f0.cpp:2:11: warning: ‘cpp11::register’ scoped attribute directive ignored [-Wattributes] 2 | void foo() {} | ^ /tmp/nix-shell.Cz8fPO/RtmpadKzBh/file16bff7121f1a99/src/cpp11.cpp: In function ‘SEXPREC* _code_16bff7617b36f0_foo()’: /tmp/nix-shell.Cz8fPO/RtmpadKzBh/file16bff7121f1a99/src/cpp11.cpp:7:30: error: invalid use of void expression 7 | return cpp11::as_sexp(foo()); | ~~~^~ make: *** [/nix/store/bb3gfb6b740ha50bbwvbgslybnqm0vgf-R-4.4.3/lib/R/etc/Makeconf:204: /tmp/nix-shell.Cz8fPO/RtmpadKzBh/file16bff7121f1a99/src/cpp11.o] Error 1 Error: Compilation failed. ``` The same behaviour happens when using an external file instead of an inline `code = ` argument. ```r packageVersion("cpp11") #> [1] ‘0.5.2’ ```