Workaround for std::logic_error in 00.08.00

Issue:
Server throws when there are no device module variables:

terminate called after throwing an instance of 'std::logic_error'
  what():  ReadAnyGroup has no element with AccessMode::wait_for_new_data.
Aborted (core dumped)

This commit introduces a workaround as proposed by jens:
  void DoocsUpdater::updateLoop(){
       if (_elementsToRead.empty()) {
           return;
       }

This commit is intended to be reverted if the above strategy has side
effects.

src/DoocsUpdater.cc

@@ -27,6 +27,10 @@ namespace ChimeraTK{
   }
 
   void DoocsUpdater::updateLoop(){
+    if (_elementsToRead.empty()) {
+        return;
+    }
+
     ReadAnyGroup group(_elementsToRead.begin(), _elementsToRead.end());
     while(true){
       auto updatedElement = group.readAny();