git-gui: Make sure remotes are loaded when picking revisions
If we are started for only a blame/browser/citool run we don't usually initialize the list of remotes, or determine which refs are tracking branches and which are local branch heads. This is because some of that work is relatively expensive and is usually not going to be needed if we are started only for a blame, or to make a single commit.
However by not loading the remote configuration we were crashing if the user tried to open a browser for another branch through the Repository menu, as our load_all_heads procedure was unable to decide which refs/heads/ items were actually local heads. We now force all remote configuration data to be loaded if we have not done so already and we are trying to create a revision mega widget.
Signed-off-by: Shawn O. Pearce <email@example.com>