Fixes Studio-42#3689, fm.sync removes unavailable volumes.

This is an amendment to the previous commit. When invoking the refresh
action on a non-root folder, ElFinder also makes a "tree" request to the
server and adds all root volumes it currently knows about. Sinc other
parts of the code might rely upon this behavior (such as tree.js), remove
non-existent volumes from the response to the tree command in the fm.sync
method.

js/elFinder.js

@@ -3094,9 +3094,11 @@ var elFinder = function(elm, opts, bootCallback) {
 				return c;
 			},
 			comp  = compare(),
+			odataRoots,
 			dfrd  = $.Deferred().always(function() { !reqFail && self.trigger('sync'); }),
+			tree = (! onlydir && this.ui.tree) ? 1 : 0,
 			opts = [this.request({
-				data           : {cmd : 'open', reload : 1, target : cwd, tree : (! onlydir && this.ui.tree) ? 1 : 0, compare : comp},
+				data           : {cmd : 'open', reload : 1, target : cwd, tree : tree, compare : comp},
 				preventDefault : true
 			})],
 			exParents = function() {
@@ -3188,7 +3190,14 @@ var elFinder = function(elm, opts, bootCallback) {
 			if (!self.validResponse('tree', pdata)) {
 				return dfrd.reject((pdata.norError || 'errResponse'));
 			}
-
+
+			// When tree = 1, the server will return all volumes in response to the open command.
+			// Remove volumes from the tree command that do not exist anymore.
+			if (tree && pdata && pdata.tree) {
+				odataRoots = $.map($.grep(odata.files, function(f) {return f.isroot;}), function(f) {return f.hash;});
+				pdata.tree = $.grep(pdata.tree, function(f) {return !f.isroot || odataRoots.indexOf(f.hash) >= 0;});
+			}
+
 			var diff = self.diff(odata.files.concat(pdata && pdata.tree ? pdata.tree : []), onlydir);
 
 			diff.added.push(odata.cwd);