Raise an error, if the file element in a resource file has no text.
Raise an error, if the file element in a resource file has no text.

- minor cleanups in the vicinity

mesonbuild/meson,mesonbuild/meson,mesonbuild/meson,mesonbuild/meson,mesonbuild/meson,mesonbuild/meson,mesonbuild/meson,mesonbuild/meson,mesonbuild/meson,mesonbuild/meson