Skip lone dash in arguments

Author: msimacek

graalpython/com.oracle.graal.python.shell/src/com/oracle/graal/python/shell/GraalPythonMain.java

@@ -265,6 +265,9 @@ protected List<String> preprocessArguments(List<String> givenArgs, Map<String, S
                         unrecognized.add(arg);
                     }
                     break;
+                case "-":
+                    programArgs.add(arg);
+                    break;
                 default:
                     if (!arg.startsWith("-")) {
                         inputFile = arg;