fix: use isBlank() instead of trim().isEmpty() to correctly handle unicode whitespace in JdbcChatMemoryRepository

Signed-off-by: astor-dev <orangnlp@gmail.com>

Author: astor-dev

memory/repository/spring-ai-model-chat-memory-repository-jdbc/src/main/java/org/springframework/ai/chat/memory/repository/jdbc/JdbcChatMemoryRepository.java

@@ -157,7 +157,7 @@ public Message mapRow(ResultSet rs, int i) throws SQLException {
 				case USER -> new UserMessage(content);
 				case ASSISTANT -> {
 					List<AssistantMessage.ToolCall> toolCalls = List.of();
-					if (toolCallsJson != null && !toolCallsJson.trim().isEmpty()) {
+					if (toolCallsJson != null && !toolCallsJson.isBlank()) {
 						try {
 							toolCalls = ModelOptionsUtils.OBJECT_MAPPER.readValue(toolCallsJson,
 									ModelOptionsUtils.OBJECT_MAPPER.getTypeFactory()