Hygiene, set unconsumed slot exactly once for each branch

in _warc_read().  Also kick __archive_read_consume() because the writer
will consume the bytes for us.  So for the EOF case, set unconsumed to 0,
for the non-EOF case set unconsumed to the minimum of the number of bytes
read and the content length.

Author: hroptatyr

libarchive/archive_read_support_format_warc.c

@@ -326,17 +326,13 @@ _warc_read(struct archive_read *a, const void **buf, size_t *bsz, int64_t *off)
 	const char *rab;
 	ssize_t nrd;
 
-	if (w->unconsumed) {
-		__archive_read_consume(a, w->unconsumed);
-		w->unconsumed = 0U;
-	}
-
 	if (w->cntoff >= w->cntlen) {
 	eof:
 		/* it's our lucky day, no work, we can leave early */
 		*buf = NULL;
 		*bsz = 0U;
-		*off = w->cntoff;
+		*off = w->cntoff + 4U/*for \r\n\r\n separator*/;
+		w->unconsumed = 0U;
 		return (ARCHIVE_EOF);
 	}