input_log: handle deferred chunk creation in threaded inputs with conditional routing

Modify route_payload_apply_outputs() to gracefully handle the case where
chunks don't exist yet in threaded mode due to asynchronous ring buffer
processing. This prevents data loss for threaded inputs using conditional
routing by falling back to normal routing instead of treating missing chunks
as fatal errors.

Signed-off-by: Eduardo Silva <eduardo@chronosphere.io>

Author: edsiper

src/flb_input_log.c

@@ -115,7 +115,14 @@ static int route_payload_apply_outputs(struct flb_input_instance *ins,
                              (void **) &chunk,
                              &out_size);
     if (ret == -1 || !chunk || !chunk->routes_mask) {
-        return -1;
+        /* For threaded inputs, chunk may not exist yet - this is expected */
+        if (flb_input_is_threaded(ins)) {
+            /* In threaded mode, routing will be handled when chunk is materialized */
+            flb_plg_debug(ins, "chunk not yet materialized for threaded input, "
+                               "routing will be handled asynchronously");
+            return 0;  /* Success - don't treat as error */
+        }
+        return -1;  /* Error for non-threaded inputs */
     }
 
     memset(chunk->routes_mask, 0, sizeof(flb_route_mask_element) * ins->config->route_mask_size);