Fix gradient mask values range (#6688)

## Summary

Gradient mask node outputs mask tensor with values in range [-1, 1],
which unexpected range for mask.
It handled in denoise node the way it translates to [0, 2] mask, which
looks even more wrongly)
From discussion with @dunkeroni I understand him as he thought that
negative values will be treated same as 0, so clamping values not change
intended node logic.

## Related Issues / Discussions

#6643 

## QA Instructions

\-

## Merge Plan

\-

## Checklist

- [x] _The PR has a short but descriptive title, suitable for a
changelog_
- [ ] _Tests added / updated (if applicable)_
- [ ] _Documentation added / updated (if applicable)_

invokeai/app/invocations/create_gradient_mask.py

@@ -39,7 +39,7 @@ class GradientMaskOutput(BaseInvocationOutput):
     title="Create Gradient Mask",
     tags=["mask", "denoise"],
     category="latents",
-    version="1.1.0",
+    version="1.2.0",
 )
 class CreateGradientMaskInvocation(BaseInvocation):
     """Creates mask for denoising model run."""
@@ -93,6 +93,7 @@ class CreateGradientMaskInvocation(BaseInvocation):
 
             # redistribute blur so that the original edges are 0 and blur outwards to 1
             blur_tensor = (blur_tensor - 0.5) * 2
+            blur_tensor[blur_tensor < 0] = 0.0
 
             threshold = 1 - self.minimum_denoise