fix CalendarUpdateFeeds causing warnings in logs

docs/changelog/7.x.x.txt

@@ -1,4 +1,5 @@
 7.5.1
+ - fix: CalendarUpdateFeeds workflow causes errors in log
  - rfe: maintenance - turn on/off maintenance mode from the command line
  - Slight performance increase in asset queries.
  - fix: Pluggable URL handlers didn't work with gateways other than /.

lib/WebGUI/Workflow/Activity/CalendarUpdateFeeds.pm

@@ -168,7 +168,7 @@ sub execute {
                     # Flush old entry
                     # KEY;ATTRIBUTE=VALUE;ATTRIBUTE=VALUE:KEYVALUE
                     my ($key_attrs,$value) = split /:/,$current_entry,2;
-                    my @attrs   = split /;/, $key_attrs;
+                    my @attrs   = $key_attrs ? (split /;/, $key_attrs) : ();
                     my $key     = shift @attrs;
                     my %attrs;
                     while (my $attribute = shift @attrs) {