fix uninitialized value error

diff --git a/index.cgi b/index.cgi
index 0179860..7cce5c6 100755 (executable)
--- a/index.cgi
+++ b/index.cgi
@@ -91,7 +91,8 @@ $increment = 0.5;
 $showstart = 12;
 
 $cgi = new CGI;
-if ( $cgi->param('showstart') =~ /^(\d+)$/ ) {
+if ( defined($cgi->param('showstart'))
+     && $cgi->param('showstart') =~ /^(\d+)$/ ) {
   die unless $1 < 24;
   $showstart = $1;
 }