Annotations without target selector cannot be edited

[lutzhelm]

The plugin currently allows saving annotations without selecting a target region on the Canvas. This would be fine (I think), but the annotation can not be edited because an error occurs in the AnnotationCreation constructor. props.annotation.target.selector` is undefined in the following line:

mirador-annotations/src/AnnotationCreation.js

Line 62 in d6b55e0

annoState.svg = props.annotation.target.selector.value;

I'd suggest to just put a check for props.annotation.target.selector around this block:

mirador-annotations/src/AnnotationCreation.js

Lines 53 to 63 in d6b55e0

	if (Array.isArray(props.annotation.target.selector)) {
	props.annotation.target.selector.forEach((selector) => {
	if (selector.type === 'SvgSelector') {
	annoState.svg = selector.value;
	} else if (selector.type === 'FragmentSelector') {
	annoState.xywh = selector.value.replace('xywh=', '');
	}
	});
	} else {
	annoState.svg = props.annotation.target.selector.value;
	}

Alternatively, saving an annotation without a selector should not be allowed. But if an annotation store provides annotations from a different source than Mirador, the error might still occur.