Fix Cannot read properties of undefined (reading 'occluded')

[klakhov]

Motivation and context

Fixes a crash when placing a pasted mask if the brush toolset is reconfigured while the paste is still in progress:

Cannot read properties of undefined (reading 'occluded')

Reproduction:

1. Create a mask and finish it.
2. Copy it (start a paste).
3. Press the brush tool in the toolbar before clicking to place the mask.
4. Click on the canvas to place it.

Root cause: pasting a mask starts the insertion pipeline in MasksHandlerImpl.draw(), which sets isInsertion = true and stores this.drawData (containing initialState). While that insertion is still live, the brush toolset legitimately re-issues canvasInstance.draw({ enabled: true, shapeType: 'mask', ... }) on brush size/tool changes but without initialState. That second call fell through to the drawing branch and unconditionally ran this.drawData = drawData, wiping out initialState while isInsertion stayed true. The next mouse:down then read this.drawData.initialState.occluded on undefined and threw.

This only affects masks because they are the only shape whose toolset reconfigures the active draw() mid-insertion; insertion also reports as Mode.DRAW, so only the canvas (which owns the private isInsertion flag) can distinguish a paste from a fresh draw. The fix therefore lives in cvat-canvas and makes draw() robust to reconfiguration calls during an active insertion:

• capture whether an insertion was already running before the call,
• skip the brush/drawing pipeline init while inserting,
• preserve the insertion's drawData (and its initialState) until the insertion actually ends.

Checklist

• I submit my changes into the develop branch
• I have created a changelog fragment
• I have updated the documentation accordingly
• I have added tests to cover my changes
• I have linked related issues

License

• I submit my code changes under the same MIT License that covers the project.