Fix bug in on_header callback when no Content-Type is found in headers

01d6ee176d modified our header-parsing
callback to parse the headers for the encoding. However, this did not
take into account the cases in which there is a 30x redirect with no
Content-Type header. In these cases, we fail to reset the values we use
to track both a) the headers and b) whether or not we've parsed the HTTP
status code, leading to a ValueError when the HTTP status line is passed
to the callback after following the redirect.

This commit fixes this case by detecting the blank line at the end of
the HTTP headers, and if no Content-Type has been found, the tracking
values are reset so that we properly process the headers post-redirect.

salt/fileclient.py

@@ -621,6 +621,13 @@ class Client(object):
 
             def on_header(hdr):
                 if write_body[1] is not False and write_body[2] is None:
+                    if not hdr.strip() and 'Content-Type' not in write_body[1]:
+                        # We've reached the end of the headers and not yet
+                        # found the Content-Type. Reset the values we're
+                        # tracking so that we properly follow the redirect.
+                        write_body[0] = None
+                        write_body[1] = False
+                        return
                     # Try to find out what content type encoding is used if
                     # this is a text file
                     write_body[1].parse_line(hdr)  # pylint: disable=no-member