Avoid 'Use of unitialized value' warning when 'pandoc_math' is not configured

diff --git a/pandoc.pm b/pandoc.pm
index 15f1b6bcc872cec67a128739f1781a484447a6a7..e9486be7cfe840198210759ab8ad5bc07212bff7 100755 (executable)
--- a/pandoc.pm
+++ b/pandoc.pm
@@ -266,7 +266,7 @@ sub htmlize ($@) {
         jsmath mathjax latexmathml asciimathml mathml katex mimetex webtex
     );
     my %with_urls = qw/mimetex 1 webtex 1/;
-    my $mathopt = $1 if $config{pandoc_math} =~ /(\w+)/;
+    my $mathopt = $1 if $config{pandoc_math} && $config{pandoc_math} =~ /(\w+)/;
     my $custom_js = $config{pandoc_math_custom_js} || '';
     if ($mathopt && $mathconf{$mathopt}) {
         if ($with_urls{$mathopt} && $custom_js) {