[pangomm] docs/reference/meson.build: Check if perl is found

[Kjell Ahlstedt <kjellahl src gnome org>]

commit 7246492c6e3382e82c5fa6a7843a14053be2f822
Author: Kjell Ahlstedt <kjellahlstedt gmail com>
Date:   Thu Jan 2 20:03:16 2020 +0100

    docs/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

 docs/reference/meson.build | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/docs/reference/meson.build b/docs/reference/meson.build
index eaa9a44..ffd535b 100644
--- a/docs/reference/meson.build
+++ b/docs/reference/meson.build
@@ -45,7 +45,7 @@ doc_conf_data.set('abs_top_builddir', built_files_root)
 doc_conf_data.set('abs_top_srcdir', project_source_root)
 doc_conf_data.set('PANGOMM_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',