get-with-headers: don't block indefinitely if the server had an internal error

If the server had an internal error and returned 500, there's nothing
to read, so "response.read()" blocks indefinitely.  Only output the
response if there's really a response.

tests/get-with-headers.py

@@ -1,60 +1,61 b''
 #!/usr/bin/env python
 
 """This does HTTP GET requests given a host:port and path and returns
 a subset of the headers plus the body of the result."""
 
 import httplib, sys
 
 try:
     import msvcrt, os
     msvcrt.setmode(sys.stdout.fileno(), os.O_BINARY)
     msvcrt.setmode(sys.stderr.fileno(), os.O_BINARY)
 except ImportError:
     pass
 
 twice = False
 if '--twice' in sys.argv:
     sys.argv.remove('--twice')
     twice = True
 headeronly = False
 if '--headeronly' in sys.argv:
     sys.argv.remove('--headeronly')
     headeronly = True
 
 reasons = {'Not modified': 'Not Modified'} # python 2.4
 
 tag = None
 def request(host, path, show):
     assert not path.startswith('/'), path
     global tag
     headers = {}
     if tag:
         headers['If-None-Match'] = tag
 
     conn = httplib.HTTPConnection(host)
     conn.request("GET", '/' + path, None, headers)
     response = conn.getresponse()
     print response.status, reasons.get(response.reason, response.reason)
     if show[:1] == ['-']:
         show = sorted(h for h, v in response.getheaders()
                       if h.lower() not in show)
     for h in [h.lower() for h in show]:
         if response.getheader(h, None) is not None:
             print "%s: %s" % (h, response.getheader(h))
     if not headeronly:
         print
-        data = response.read()
-        sys.stdout.write(data)
+        if response.status != 500:
+            data = response.read()
+            sys.stdout.write(data)
 
         if twice and response.getheader('ETag', None):
             tag = response.getheader('ETag')
 
     return response.status
 
 status = request(sys.argv[1], sys.argv[2], sys.argv[3:])
 if twice:
     status = request(sys.argv[1], sys.argv[2], sys.argv[3:])
 
 if 200 <= status <= 305:
     sys.exit(0)
 sys.exit(1)