restripe: fix ignoring return value of ‘read’ and lseek
Got below error when run "make everything".
restripe.c: In function ‘test_stripes’:
restripe.c:870:4: error: ignoring return value of ‘read’, declared with attribute warn_unused_result [-Werror=unused-result]
read(source[i], stripes[i], chunk_size);
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Fix it by check the return value of ‘read’, and free memory
in the failure case.
And check the return value of lseek as well per Jes's comment.