Cygwin: pipe: Fix hang due to inadvertent 0-length raw_write()

It is possible for `NtQueryInformationFile()` to report a 0-length
`InboundQuota` when obtaining `FilePipeLocalInformation`. This seems to
be the case e.g. when a pipe was created on the other side and its quota
information is not available on the client side.

This can lead to a situation where the `avail` variable is set to 0, and
since that is used to cap the number of bytes to send, a 0-length write.
Which hangs forever.

This was observed in the MSYS2 project when building GIMP, and reduced
to a simple test case where a MINGW `ninja.exe` tries to call an MSYS
`bison.exe` and the error message (saying that `bison` wants to have
some input) is not even shown.

Since the minimal pipe buffer size is 4k, let's ensure that it is at
least that, even when `InboundQuota` reports 0.

This fixes msys2/msys2-runtime#270

Fixes: cbfaeba (Cygwin: pipe: Fix incorrect write length in raw_write())
Helped-by: Corinna Vinschen <[email protected]>
Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

winsup/cygwin/fhandler/pipe.cc

@@ -1158,7 +1158,7 @@ fhandler_pipe::set_pipe_buf_size ()
   status = NtQueryInformationFile (get_handle (), &io, &fpli, sizeof fpli,
 				   FilePipeLocalInformation);
   if (NT_SUCCESS (status))
-    pipe_buf_size = fpli.InboundQuota;
+    pipe_buf_size = fpli.InboundQuota < PIPE_BUF ? PIPE_BUF : fpli.InboundQuota;
 }
 
 int