fix(ui): hide CoreProgressBar progression in indeterminate state

I forgot to hide the progression when the `CoreProgressBar`'s
progression is `undefined` (which is the case in "indeterminate" state
when no `value` is provided).

So it actually displays `NaN%` when the component settings are `value
=== undefined && displayPercentage === true`. It's better to simply not
display the percentage in this situation.

src/ui/src/components/core/content/CoreProgressBar.vue

@@ -18,7 +18,7 @@
 				label
 			}}</label>
 			<span
-				v-if="displayPercentage"
+				v-if="displayPercentage && progression !== undefined"
 				class="CoreProgressBar__title__progress"
 				>{{ progressionText }}</span
 			>