Spring-ai GH-876: stream.content() swallowing blank space

• Fixing an issue where calling stream.content() method swallows leading blank spaces.

Resolves https://github.com/spring-projects/spring-ai/issues/1089 Resolves https://github.com/spring-projects/spring-ai/issues/1089

Comment From: tzolov

LGTM, thanks @sobychacko

Comment From: tzolov

rebased and merged at 9aee4aac4c805c2810e3ff9a076113b47179ba38