Tweak removeFilePathRecursively handling of empty path

Author: PicoCreator

src/main/java/picoded/dstack/mongodb/MongoDB_FileWorkspaceMap.java

@@ -261,7 +261,7 @@ protected void removeFilePathRecursively(String oid, String path) {
 		// Lets build the query for the "root file"
 		Bson query = null;
 
-		if( path == null ) {
+		if( path == null || path.equals("/") || path.isEmpty() ) {
 			// Remove everything under the oid
 			query = Filters.eq("metadata._oid", oid);
 		} else {