when source file doesn't exist throw proper exception

rest-api/src/main/java/lcsb/mapviewer/api/projects/ProjectController.java

@@ -123,6 +123,9 @@ public class ProjectController extends BaseController {
   public ResponseEntity<byte[]> getProjectSource(@PathVariable(value = "projectId") String projectId)
       throws QueryException {
     FileEntry file = projectController.getSource(projectId);
+    if (file == null) {
+      throw new ObjectNotFoundException("File doesn't exist");
+    }
     MediaType type = MediaType.TEXT_PLAIN;
     if (file.getOriginalFileName().endsWith("xml")) {
       type = MediaType.APPLICATION_XML;