fix: reset() crashes when no scenario is built

[andrewwhitecdw]

This PR addresses the following issue in exts/omni.ext.mobility_gen/omni/ext/mobility_gen/extension.py: reset() crashes when no scenario is built.

Changes

• exts/omni.ext.mobility_gen/omni/ext/mobility_gen/extension.py: reset() crashes when no scenario is built.

Details

Before:

    def reset(self):
        self.writer = None
        self.scenario.reset()
        if self.recording_enabled:
            self.start_new_recording()

After:

    def reset(self):
        if self.scenario is None:
            return
        self.writer = None
        self.scenario.reset()
        if self.recording_enabled:
            self.start_new_recording()