splice: reinstate SIGPIPE/EPIPE handling

splice: reinstate SIGPIPE/EPIPE handling

Commit 8924feff66f3 ("splice: lift pipe_lock out of splice_to_pipe()")
caused a regression when there were no more readers left on a pipe that
was being spliced into: rather than the expected SIGPIPE and -EPIPE
return value, the writer would end up waiting forever for space to free
up (which obviously was not going to happen with no readers around).

Fixes: 8924feff66f3 ("splice: lift pipe_lock out of splice_to_pipe()")
Reported-and-tested-by: Andreas Schwab <[email protected]>
Debugged-by: Al Viro <[email protected]>
Cc: [email protected]   # v4.9
Signed-off-by: Linus Torvalds <[email protected]>