[core/process] Fix a problem >&100 does not fail.

Author: akinomyoga

core/process.py

@@ -257,6 +257,13 @@ def _PushDup(self, fd1, loc):
         # already returned 3, e.g. echo 3>out.txt
         return NO_FD
 
+      # Check the validity of fd1 before _PushSave(fd2)
+      try:
+        fcntl.fcntl(fd1, fcntl.F_GETFD)
+      except IOError as e:
+        self.errfmt.Print('%d: %s', fd1, posix.strerror(e.errno))
+        raise
+
       need_restore = self._PushSave(fd2)
 
       #log('==== dup2 %s %s\n' % (fd1, fd2))