fix(spring-ai-openai): Prevent out-of-range errors when merging tool calls.

Auto-cherry-pick to 1.0.x
Fixes spring-projects#4229
Signed-off-by: xfl12345 <[email protected]>

Author: xfl12345

models/spring-ai-openai/src/main/java/org/springframework/ai/openai/api/OpenAiStreamFunctionCallingHelper.java

@@ -112,13 +112,13 @@ private ChatCompletionMessage merge(ChatCompletionMessage previous, ChatCompleti
 
 		List<ToolCall> toolCalls = new ArrayList<>();
 		ToolCall lastPreviousTooCall = null;
-		if (previous.toolCalls() != null) {
+		if (previous.toolCalls() != null && !previous.toolCalls().isEmpty()) {
 			lastPreviousTooCall = previous.toolCalls().get(previous.toolCalls().size() - 1);
 			if (previous.toolCalls().size() > 1) {
 				toolCalls.addAll(previous.toolCalls().subList(0, previous.toolCalls().size() - 1));
 			}
 		}
-		if (current.toolCalls() != null && current.toolCalls().size() > 0) {
+		if (current.toolCalls() != null && !current.toolCalls().isEmpty()) {
 			if (current.toolCalls().size() > 1) {
 				throw new IllegalStateException("Currently only one tool call is supported per message!");
 			}