Add function to get number of banks re #9260

This function presently only works when this number has a single digit. lexical_cast<int> does not accept space characters.

Signed-off-by: Karl Palmen <karl.palmen@stfc.ac.uk>

Code/Mantid/Framework/DataHandling/src/LoadGSASInstrumentFile.cpp

@@ -198,7 +198,7 @@ namespace DataHandling
           // line too short
           return -1;
         }
-        return  boost::lexical_cast<int>(lines[i].substr(lookFor.size(),3)); // Found
+        return  boost::lexical_cast<int>(lines[i].substr(lookFor.size()+2,1)); // Found
       }
     }
     return 0;