Add IF NOT EXISTS to index creation sql statement.

services/git-bridge/src/main/java/uk/ac/ic/wlgitbridge/writelatex/model/db/sql/update/create/CreateIndexURLIndexStore.java

@@ -10,7 +10,8 @@ import java.sql.SQLException;
  */
 public class CreateIndexURLIndexStore implements SQLUpdate {
 
-    public static final String CREATE_INDEX_URL_INDEX_STORE = "CREATE INDEX `project_path_index` ON `url_index_store`(`project_name`, `path`);\n";
+    public static final String CREATE_INDEX_URL_INDEX_STORE =
+            "CREATE INDEX IF NOT EXISTS `project_path_index` ON `url_index_store`(`project_name`, `path`);\n";
 
     @Override
     public String getSQL() {