When someone is using the TREES setting for RBTools, it's common that

they'll be using repository paths as the keys to that. In this case, a

command like rbt patch --print would fail because it was trying to

avoid initializing the scmtool, and then we never got the correct server

URL.
This makes it so if TREES is present in the configuration (and now

also actually populated with data, since the default value will be {}),

and we otherwise did not need the scmtool, we'll still attempt to

initialize it. If we get it, then great, we can use it for TREES. If we

don't, we ignore that and proceed as previous.

Ran unit tests.
Verified that when TREES was defined, we now were initializing the

  scmtool when running rbt patch --print.