Populate cable properties if length is NaN

Cable Length property value is NaN by default. The current
implementation ignores processing other remaining Cable properties
if the length is NaN. Per Ed's comment here we need to
ignore if length is NaN and continue to process remaining properties:
https://gerrit.openbmc.org/c/openbmc/bmcweb/+/50265/4..7/redfish-core\
/lib/cable.hpp#b51

Testing:
1. Validator test not done, assumed it is OK since it is a minor change
   in the code logic.

2. curl testing:
$ curl -k https://user:password@host:18080/redfish/v1/Cables/dp0_cable1


{
  "@odata.id": "/redfish/v1/Cables/dp0_cable1",
  "@odata.type": "#Cable.v1_0_0.Cable",
  "CableType": "",
  "Id": "dp0_cable1",
  "Name": "Cable"
}

Signed-off-by: Shantappa Teekappanavar <shantappa.teekappanavar@ibm.com>
Change-Id: If73828484d91bbf2eee45a31973c825bab008ba4