bitbake: data_smart: Cache the fact a variable accesses another even if its unset

If a variable references another but it isn't set at present, the
reference wasn't stored. It really should be marked as a reference
and the higher level dependency code can handle as appropriate.

(Bitbake rev: b05b748b2153c941b95cd36fb22aaafc4dbf3791)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/data_smart.py

@@ -100,8 +100,8 @@ class VariableParse:
                 self.execs |= varparse.execs
                 return varparse.value
             var = self.d.getVar(key, True)
+            self.references.add(key)
             if var is not None:
-                self.references.add(key)
                 return var
             else:
                 return match.group()