### What happened?

`_bedrock_converse_messages_pt` / `_bedrock_converse_messages_pt_async` in `litellm/litellm_core_utils/prompt_templates/factory.py` replace an empty or whitespace-only user message with a `"Please continue."` placeholder (issue #7169), because Bedrock Converse rejects blank-text `ContentBlock`s:

> The text field in the ContentBlock object at messages.X.content.0 is blank.

The substitution is computed once via `get_user_message_block_or_continue_message(...)` and returned as `message_block`. The **list-content** branch correctly builds the block from `message_block["content"]`, but the **string-content** branch reads the *original* `messages[msg_i]["content"]` instead — so for plain-string content the substitution is silently discarded and the blank/whitespace text is forwarded to Bedrock unchanged, defeating the #7169 fix.

### Minimal reproduction (offline, no network / keys)

```python import litellm from litellm.litellm_core_utils.prompt_templates.factory import _bedrock_converse_messages_pt

litellm.modify_params = True print(_bedrock_converse_messages_pt( [{"role": "user", "content": " "}], # whitespace-only string content model="anthropic.cla…