Fix status clearing with initial empty value

When selecting an emoji but not specifying a message, the internal
message value was null which caused a server validation error on
sending.

This fixes the SetStatusModal to always work with an empty string
upfront, as this is the value the field would have if edited and cleared
manually.

Signed-off-by: Vincent Petry <vincent@nextcloud.com>

apps/user_status/src/components/SetStatusModal.vue

@@ -98,7 +98,7 @@ export default {
 		return {
 			clearAt: null,
 			icon: null,
-			message: null,
+			message: '',
 			statuses: getAllStatusOptions(),
 		}
 	},
@@ -119,7 +119,7 @@ export default {
 	mounted() {
 		this.messageId = this.$store.state.userStatus.messageId
 		this.icon = this.$store.state.userStatus.icon
-		this.message = this.$store.state.userStatus.message
+		this.message = this.$store.state.userStatus.message || ''
 
 		if (this.$store.state.userStatus.clearAt !== null) {
 			this.clearAt = {