Fix crashing modifying array length

Also avoids unnecessary allocation and set.

Fixes cases like the following:
```javascript
let obj = { a: [1,2] };
dotProp.delete(obj, 'a.1');
dotProp.set(obj, 'a.length', 1);
```
Previously would throw `Uncaught RangeError: Invalid array length` when it tries to set `obj.a.length = {}`

index.js

@@ -73,12 +73,10 @@ module.exports = {
 		for (let i = 0; i < pathArray.length; i++) {
 			const p = pathArray[i];
 
-			if (!isObject(object[p])) {
-				object[p] = {};
-			}
-
 			if (i === pathArray.length - 1) {
 				object[p] = value;
+			} else if (!isObject(object[p])) {
+				object[p] = {};
 			}
 
 			object = object[p];