[mm-common] skeletonmm/doc/reference/meson.build: Check if perl is found

[Kjell Ahlstedt <kjellahl src gnome org>]

commit f9903deb9c49d9b16bae6e7ecbecfdd80b924ba9
Author: Kjell Ahlstedt <kjellahlstedt gmail com>
Date:   Thu Jan 2 20:07:25 2020 +0100

    skeletonmm/doc/reference/meson.build: Check if perl is found
    
    Don't use perl.path() when configuring Doxyfile, if perl is not found.
    Perl is not required, if build-documentation=false.
    See https://github.com/libsigcplusplus/libsigcplusplus/issues/53

 skeletonmm/doc/reference/meson.build | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/skeletonmm/doc/reference/meson.build b/skeletonmm/doc/reference/meson.build
index 9611195..7344252 100644
--- a/skeletonmm/doc/reference/meson.build
+++ b/skeletonmm/doc/reference/meson.build
@@ -44,7 +44,7 @@ doc_conf_data.set('abs_top_builddir', built_files_root)
 doc_conf_data.set('abs_top_srcdir', project_source_root)
 doc_conf_data.set('SKELETONMM_MODULE_NAME', book_name)
 doc_conf_data.set('DOXYGEN_TAGFILES', doxygen_tagfiles)
-doc_conf_data.set('PERL', perl.path())
+doc_conf_data.set('PERL', perl.found() ? perl.path() : '')
 
 configure_file(
   input: 'Doxyfile.in',