[Platform][OpenAI] Handle non-string values in StreamResult gracefully

Author: oesteve

src/agent/src/Toolbox/StreamResult.php

@@ -51,6 +51,11 @@ public function getContent(): \Generator
                 break;
             }
 
+            if (!\is_string($value)) {
+                yield $value;
+                break;
+            }
+
             $streamedResult .= $value;
 
             yield $value;