Fixes broken import in Live Visualizer image plot (#2486)

# Description

Fixes isaacsim import in the image plot function of the live
visualizers.

## Type of change

- Bug fix (non-breaking change which fixes an issue)

## Checklist

- [x] I have run the [`pre-commit` checks](https://pre-commit.com/) with
`./isaaclab.sh --format`
- [ ] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] I have updated the changelog and the corresponding version in the
extension's `config/extension.toml` file
- [x] I have added my name to the `CONTRIBUTORS.md` or my name already
exists there

Author: pascal-roth

source/isaaclab/isaaclab/ui/widgets/image_plot.py

@@ -4,13 +4,18 @@
 # SPDX-License-Identifier: BSD-3-Clause
 
 import numpy as np
+from contextlib import suppress
 from matplotlib import cm
 from typing import TYPE_CHECKING, Optional
 
 import carb
 import omni
 import omni.log
 
+with suppress(ImportError):
+    # isaacsim.gui is not available when running in headless mode.
+    import isaacsim.gui.components.ui_utils
+
 from .ui_widget_wrapper import UIWidgetWrapper
 
 if TYPE_CHECKING: