[OSSTEST PATCH 06/12] duration estimator: Fix a warning

[Ian Jackson <ian.jackson@xxxxxxxxxxxxx>]

$onhost can be undef.  Fixes this warning:

Use of uninitialized value $onhost in concatenation (.) or string at 
Osstest/Executive.pm line 1293.

Signed-off-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
---
 Osstest/Executive.pm | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/Osstest/Executive.pm b/Osstest/Executive.pm
index 4151aa6c..b3aecfc5 100644
--- a/Osstest/Executive.pm
+++ b/Osstest/Executive.pm
@@ -1274,7 +1274,8 @@ END
     return sub {
         my ($job, $hostidname, $onhost, $uptoincl_testid) = @_;
 
-       my $memokey = "$job $hostidname $onhost ".($uptoincl_testid//"");
+       my $memokey =
+         "$job $hostidname ".($onhost//"")." ".($uptoincl_testid//"");
        my $memo = $our_memo->{$memokey};
        return @$memo if $memo;
 
-- 
2.20.1