When a reasoning model returns a response consisting solely of
<think>...</think> content, the emptiness guard fired before
strip_think_content ran, so the node silently returned an empty
string rather than signalling an error. Add a post-strip check
in both LMStudioTextGen and LMStudioImageToText that raises
ValueError if strip_think_content reduces the text to nothing.
Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>