Enter Browse mode before switching API server

(Because if in Select mode, the selected entity will be missing
and cause an error to be thrown)

js/id/ui/source_switch.js

@@ -13,6 +13,7 @@ iD.ui.SourceSwitch = function(context) {
         context.connection()
             .switch(live ? keys[1] : keys[0]);
 
+        context.enter(iD.modes.Browse(context));
         context.flush();
 
         d3.select(this)