Fix a compression bug

do_ssl3_write() was crashing when compression was enabled. We calculate
the maximum length that a record will be after compression and reserve
those bytes in the WPACKET. Unfortunately we were adding the maximum
compression overhead onto the wrong variable resulting in a corrupted
record.
Reviewed-by: NRich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/2814)

ssl/record/rec_layer_s3.c

@@ -791,7 +791,7 @@ int do_ssl3_write(SSL *s, int type, const unsigned char *buf,
 
         maxcomplen = pipelens[j];
         if (s->compress != NULL)
-            pipelens[j] += SSL3_RT_MAX_COMPRESSED_OVERHEAD;
+            maxcomplen += SSL3_RT_MAX_COMPRESSED_OVERHEAD;
 
         /* write the header */
         if (!WPACKET_put_bytes_u8(thispkt, rectype)