Add exception printout for missing ConfigReader

This is to support when running under Boost::Test which will swallow the
message otherwise and print the confusing ~AppBase() message of not
being properly shut down

src/ModuleImpl.cc

@@ -39,8 +39,13 @@ namespace ChimeraTK {
       instance = dynamic_cast<ConfigReader*>(mod);
     }
     if(nConfigReaders != 1) {
-      throw ChimeraTK::logic_error("ApplicationModule::appConfig() called but " + std::to_string(nConfigReaders) +
-          " instances of ChimeraTK::ConfigReader have been found.");
+      std::string message = "ApplicationModule::appConfig() called but " + std::to_string(nConfigReaders) +
+                            " instances of ChimeraTK::ConfigReader have been found.";
+      // Printing the message as well; there is a situation when running under Boost::Test where this
+      // is caught by Boost and causes a weird destructor message from AppBase.cc instead with no means of
+      // finding out the actual error
+      std::cerr << message << std::endl;
+      throw ChimeraTK::logic_error(message);
     }
     return *instance;
   }