in_exec_wasi: fix possible NULL deref

`tmpfile()` can return NULL and this is not checked for at the moment.
If indeed it returns NULL then the call on line 70 `fileno(stdoutp)`
will cause a NULL dereference.

Signed-off-by: David Korczynski <[email protected]>

Author: DavidKorczynski

plugins/in_exec_wasi/in_exec_wasi.c

@@ -59,6 +59,11 @@ static int in_exec_wasi_collect(struct flb_input_instance *ins,
     size_t out_size = 0;
     struct flb_time out_time;
 
+    /* Validate the temporary file was created */
+    if (stdoutp == NULL) {
+        return -1;
+    }
+
     if (ctx->oneshot == FLB_TRUE) {
         ret = flb_pipe_r(ctx->ch_manager[0], &val, sizeof(val));
         if (ret == -1) {