fix(ui): fix double uploading file from channels upload form

Part-of: <https://dev.funkwhale.audio/funkwhale/funkwhale/-/merge_requests/2307>

front/src/components/channels/UploadForm.vue

@@ -153,7 +153,7 @@ const beforeFileUpload = (newFile: VueUploadItem) => {
   if (remainingSpace.value < (newFile.size ?? Infinity) / 1e6) {
     newFile.error = 'denied'
   } else {
-    upload.value.active = true
+    newFile.active = true
   }
 }
 

front/src/components/channels/UploadMetadataForm.vue

@@ -22,7 +22,7 @@ const props = withDefaults(defineProps<Props>(), {
 })
 
 const newValues = reactive<Values>({
-  ...(props.values ?? props.upload.import_metadata ?? {}) as Values
+  ...(props.values ?? props.upload.import_metadata ?? { description: '' }) as Values
 })
 
 const isLoading = computed(() => !props.upload)