Double JSON ecode prompt data

The python JSON module produces output with NaN values that javascript
refuses to consider valid JSON. As a workaround, the prompt data, which
has never been used, is now json encoded before being added as metadata

Resolves #282

Author: AustinMroz

videohelpersuite/nodes.py

@@ -308,7 +308,7 @@ def batched_encode(images, vae, frames_per_batch):
         video_metadata = {}
         if prompt is not None:
             metadata.add_text("prompt", json.dumps(prompt))
-            video_metadata["prompt"] = prompt
+            video_metadata["prompt"] = json.dumps(prompt)
         if extra_pnginfo is not None:
             for x in extra_pnginfo:
                 metadata.add_text(x, json.dumps(extra_pnginfo[x]))