vis: correctly close pipe connected to stdin of external process

Once we have written all data we should properly close the (correct)
pipe. Before we wrongly closed the pipe connected to the standard output
stream.

More generally, we currently do not listen for child process termination,
but instead wait until all the connected pipes are closed. This might
be problematic in case the external process keeps hold of the standard
I/O file descriptors. One particular example of this is wl-copy(1).

See martanne#929

vis.c

@@ -1860,8 +1860,8 @@ int vis_pipe(Vis *vis, File *file, Filerange *range, const char *argv[],
 			if (len > 0) {
 				rout.start += len;
 				if (text_range_size(&rout) == 0) {
-					close(pout[1]);
-					pout[1] = -1;
+					close(pin[1]);
+					pin[1] = -1;
 				}
 			} else {
 				close(pin[1]);