replace remaining dummy error with exception

File.cpp

@@ -196,8 +196,7 @@ bool File::next() {
             continue;
           }
 
-          std::cerr << "ERROR 5" << std::endl;
-          exit(0);
+          throw XmlFileException("expected attribute key char or =");
 
         case AFTER_ATTRKEY:
           if (std::isspace(c))