HTTP: Don't attempt to needlessly decompress redirect body

This change fixes a regression where redirect body would needlessly be
decompressed even though it was to be ignored anyway. As it happens this
causes secondary issues since there appears to be a bug in apache2 that
it in certain conditions generates a corrupt zlib response. The
regression was created by commit:
dbcced8e32

Discovered-by: Harry Sintonen
Closes #2798

lib/transfer.c

@@ -797,7 +797,7 @@ static CURLcode readwrite_data(struct Curl_easy *data,
                                            nread);
             }
           }
-          else
+          else if(!k->ignorebody)
             result = Curl_unencode_write(conn, k->writer_stack, k->str, nread);
         }
         k->badheader = HEADER_NORMAL; /* taken care of now */