Fixed duplicate if error reported by cppcheck. Refs #8881.

Code/Mantid/Framework/Algorithms/src/SaveGSASInstrumentFile.cpp

@@ -140,11 +140,11 @@ ChopperConfiguration::ChopperConfiguration(const int freq, const std::string& ba
   size_t numbanks = m_bankIDs.size();
 
   // Check size
-  if (m_vecCWL.size() != numbanks || m_vecCWL.size() != numbanks || m_vecCWL.size() != numbanks)
+  if (m_vecCWL.size() != numbanks || m_mindsps.size() != numbanks || m_maxdsps.size() != numbanks 
+          || m_maxtofs.size() != numbanks)
   {
-    stringstream errss;
-    errss << "Default chopper constants have different number of elements. ";
-    throw runtime_error(errss.str());
+    std::string errmsg("Default chopper constants have different number of elements. ");
+    throw runtime_error(errmsg);
   }
 
   // Set up index map