[tig PATCH] continue updates when pipe read has errno "Success"

When we are reading from a pipe and receive a signal, our read call fails and ferror() returns true. The current behavior is to call end_update and report failure. However, we can detect this situation by checking that errno is set to success and continue the reading process.

You can provoke this behavior by running a "tig blame" that takes a few seconds and then resizing the terminal that tig is running in (you should get an incomplete blame output and the error "Failed to read: Success").

Signed-off-by: Jeff King <peff@peff.net>
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I am not convinced this is the right solution. Specifically:

  - there are a few other calls to ferror. Maybe they should be
    converted, too, which implies that perhaps there is a better idiom
    for checking this.

  - I have no idea how portable this is. Do all stdio implementations
    fail to restart on signal? Do they all set ferror and have errno ==
    0 (I would have expected EINTR, or at the very least a 0-read
    without ferror set)?

But it works for me (Linux, glibc 2.7).

 tig.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)