Bug fixed CRAM decoding for CRAM 2.1.

Commit cf68cd3 moved the crc checking to the uncompress function so it
only checked validity of the data used (incase we're decoding only
some fields) and so that CRC checking is part of the multi-threaded
code.  Unfortunately this had the side effect of attempting to
validate CRCs on older file format versions where they were not
present.

Author: jkbonfield

io_lib/cram_io.c

@@ -1532,6 +1532,8 @@ cram_block *cram_read_block(cram_fd *fd) {
 	// Check later, if and only if we do decompression of this block
 	b->crc32_checked = fd->ignore_md5;
 	b->crc_part = crc;
+    } else {
+	b->crc32_checked = 1; // CRC not present
     }
 
     b->orig_method = b->method;