nilrt.inc: Conditionally set PACKAGE_FEED_URIS_ADDITIONAL[NI-dist]
nilrt.inc: Conditionally set PACKAGE_FEED_URIS_ADDITIONAL[NI-dist]

Only set if the variable value is not already set. This allows the
dist feed to be replaced with a different URI at azdo build time.

Signed-off-by: Shruthi Ravichandran <shruthi.ravichandran@ni.com>

Rebased-by: Alex Stewart <04cdb2793e4fb0120cc30d1c823099f3862701f4@ni.com>
* Fix patch context.

ni/meta-nilrt,ni/meta-nilrt,ni/meta-nilrt,ni/meta-nilrt,ni/meta-nilrt