HPCC-11446 ECL Watch build issues prevent site creation

If there is any build error during the eclwatch package step, it will prevent
stub.htm from being copied.  This prevents the entire site from displaying.

Fixes HPCC-11446

Signed-off-by: Gordon Smith <gordon.smith@lexisnexis.com>
Merge pull request #5885 from GordonSmith/HPCC-11446

HPCC-11446 ECL Watch build issues prevent site creation

Reviewed-By: Xiaoming Wang <xiaoming.wang@lexisnexis.com>
Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>