Revert "exec: Don't flush if the user says no to -ok"

From the bfs_ctx_flush() implementation:

    // Before executing anything, flush all open streams.  This ensures that
    // - the user sees everything relevant before an -ok[dir] prompt

But that only works if we call it before the prompt.

This reverts commit 21344df.

src/exec.c

@@ -352,6 +352,9 @@ static void bfs_exec_closewd(struct bfs_exec *execbuf, const struct BFTW *ftwbuf
 
 /** Actually spawn the process. */
 static int bfs_exec_spawn(const struct bfs_exec *execbuf) {
+	// Flush the context state for consistency with the external process
+	bfs_ctx_flush(execbuf->ctx);
+
 	if (execbuf->flags & BFS_EXEC_CONFIRM) {
 		for (size_t i = 0; i < execbuf->argc; ++i) {
 			if (fprintf(stderr, "%s ", execbuf->argv[i]) < 0) {
@@ -368,9 +371,6 @@ static int bfs_exec_spawn(const struct bfs_exec *execbuf) {
 		}
 	}
 
-	// Flush cached state for consistency with the external process
-	bfs_ctx_flush(execbuf->ctx);
-
 	if (execbuf->flags & BFS_EXEC_MULTI) {
 		bfs_exec_debug(execbuf, "Executing '%s' ... [%zu arguments] (size %zu)\n",
 		               execbuf->argv[0], execbuf->argc - 1, execbuf->arg_size);

tests/gnu/exec_flush.sh

@@ -1,4 +1,4 @@
-# IO streams should be flushed before executing programs
+# I/O streams should be flushed before executing programs
 invoke_bfs basic -print0 -exec echo found \; | tr '\0' ' ' >"$OUT"
 sort_output
 diff_output

tests/gnu/ok_flush.out

@@ -0,0 +1,19 @@
+basic ? found
+basic/a ? found
+basic/b ? found
+basic/c ? found
+basic/c/d ? found
+basic/e ? found
+basic/e/f ? found
+basic/g ? found
+basic/g/h ? found
+basic/i ? found
+basic/j ? found
+basic/j/foo ? found
+basic/k ? found
+basic/k/foo ? found
+basic/k/foo/bar ? found
+basic/l ? found
+basic/l/foo ? found
+basic/l/foo/bar ? found
+basic/l/foo/bar/baz ? found

tests/gnu/ok_flush.sh

@@ -0,0 +1,4 @@
+# I/O streams should be flushed before -ok prompts
+yes | invoke_bfs basic -printf '%p ? ' -ok echo found \; 2>&1 | tr '\0' ' ' | sed 's/?.*?/?/' >"$OUT"
+sort_output
+diff_output