Disallow whitespace in composer aliases

These cause problems with the composer alias parsing code.
If an alias from the config file has whitespace, only the first word
will be taken into account (ignoring any leading or trailing whitespace).

src/gui/Pages/Chat/Composer/MessageArea.qml

@@ -19,14 +19,16 @@ HTextArea {
     property bool textChangedSinceLostFocus: false
 
     readonly property var usableAliases: {
-        const obj = {}
+        const obj     = {}
+        const aliases = window.settings.writeAliases
 
         // Get accounts that are members of this room with permission to talk
-        for (const [id, alia] of Object.entries(window.settings.writeAliases)){
+        for (const [id, alias] of Object.entries(aliases)) {
             const room = ModelStore.get(id, "rooms").find(chat.roomId)
-            if (room &&
-                    ! room.inviter_id && ! room.left && room.can_send_messages)
-                obj[id] = alia
+
+            room && ! room.inviter_id && ! room.left && room.can_send_messages?
+            obj[id] = alias.trim().split(/\s/)[0] :
+            null
         }
 
         return obj