Spring-ai Fix the Options merging logic in the OpenAiImageClient#call

Current options merging behaviour in: https://github.com/spring-projects/spring-ai/blob/c1d30345698cad439a4789e3255e22cedc07c062/models/spring-ai-openai/src/main/java/org/springframework/ai/openai/OpenAiImageClient.java#L59-L82 seems incorrect.

There are at least two options-to-use variables and one of them (optionsToUse) is never used.