create_pen_list: only print if values are set

On a failed download of the PEN list, the create_pen_list script
improperly printed an invalid entry of { , "" } causing the build to
fail. The last line print must check that it has something to print or
it will print the wrong thing.

Partially resolves ipmitool/ipmitool#11

Signed-off-by: Vernon Mauery <vernon.mauery@intel.com>

lib/create_pen_list

@@ -67,7 +67,9 @@ parse_pen_list() {
       }
 
       END {
+          if(PEN) {
             print "{ " PEN ", \"" ENTERPRISE "\" },"
+          }
       }'
 }