fix TypeError spam when opening QML

[hannesdelbeke]

this PR fixes the following: when opening QML the console always spams errors

Entering state: "initialising"
Entering state: "collecting"
WARN (bpy.rna): C:\Users\blender\git\blender-v300\blender.git\source\blender\python\intern\bpy_rna.c:1352 pyrna_enum_to_py: current value '0' matches no enum in 'ColorManagedInputColorspaceSettings', '(null)', 'name'
Not ready, hold SHIFT to force an exit
Spent 1286.91 ms resetting
Made 0 requests during publish.
file:///C:/Users/REDACTED/pyblish_qml/qml/List.qml:28: TypeError: Cannot read property 'width' of null
file:///C:/Users/REDACTED/pyblish_qml/qml/List.qml:28: TypeError: Cannot read property 'width' of null
file:///C:/Users/REDACTED/pyblish_qml/qml/List.qml:28: TypeError: Cannot read property 'width' of null
file:///C:/Users/REDACTED/pyblish_qml/qml/List.qml:28: TypeError: Cannot read property 'width' of null
file:///C:/Users/REDACTED/pyblish_qml/qml/List.qml:28: TypeError: Cannot read property 'width' of null
file:///C:/Users/REDACTED/pyblish_qml/qml/List.qml:28: TypeError: Cannot read property 'width' of null
file:///C:/Users/REDACTED/pyblish_qml/qml/List.qml:28: TypeError: Cannot read property 'width' of null
file:///C:/Users/REDACTED/pyblish_qml/qml/List.qml:28: TypeError: Cannot read property 'width' of null
file:///C:/Users/REDACTED/pyblish_qml/qml/List.qml:28: TypeError: Cannot read property 'width' of null
file:///C:/Users/REDACTED/pyblish_qml/qml/List.qml:28: TypeError: Cannot read property 'width' of null
file:///C:/Users/REDACTED/pyblish_qml/qml/List.qml:28: TypeError: Cannot read property 'width' of null
file:///C:/Users/REDACTED/pyblish_qml/qml/List.qml:28: TypeError: Cannot read property 'width' of null

[mottosso]

Nice one 🥳