Fix integer overflow in cram_compress_block2

The figure used here is somewhat arbitrary as it's simply a marker for
something considerably worse than no compression, given it's used in
places where the compression wasn't applied or fails.  Although sz is
long, it may get other modifiers and the CRAM block size is int so
UINT_MAX seems like a natural "larger than possible" value to use.

Credit to OSS-Fuzz
Fixes oss-fuzz 64616

cram/cram_io.c

@@ -2079,10 +2079,10 @@ int cram_compress_block2(cram_fd *fd, cram_slice *s,
                     } else if (c) {
                         free(c);
                     } else {
-                        sz[m] = b->uncomp_size*2+1000; // arbitrarily worse than raw
+                        sz[m] = UINT_MAX; // arbitrarily worse than raw
                     }
                 } else {
-                    sz[m] = b->uncomp_size*2+1000; // arbitrarily worse than raw
+                    sz[m] = UINT_MAX; // arbitrarily worse than raw
                 }
             }