Fix empty inner blocks for template.

[tcmulder]

This doesn't work:

const innerBlocksProps = useInnerBlocksProps({
    template: [['core/paragraph']],
});

Either this does:

const innerBlocksProps = useInnerBlocksProps({}, {
    template: [['core/paragraph']],
});

Or, better yet, though it requires some additional refactoring (think through the logic, since blockProps I don't think is being used correctly currently):

const innerBlocksProps = useInnerBlocksProps(blockProps, {
    template: [['core/paragraph']],
});