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/AccountSettings/Account.qml

@@ -74,7 +74,7 @@ HFlickableColumnPage {
             enabled:
                 avatar.changed ||
                 nameField.item.changed ||
-                (aliasField.item.changed && ! aliasField.alreadyTakenBy)
+                (aliasField.item.changed && ! aliasField.item.error)
 
             onClicked: applyChanges()
         }
@@ -235,6 +235,8 @@ HFlickableColumnPage {
         readonly property var aliases: window.settings.writeAliases
         readonly property string currentAlias: aliases[userId] || ""
 
+        readonly property bool hasWhiteSpace: /\s/.test(item.text)
+
         readonly property string alreadyTakenBy: {
             if (! item.text) return ""
 
@@ -247,8 +249,8 @@ HFlickableColumnPage {
         label.text: qsTr("Composer alias:")
 
         errorLabel.text:
-            alreadyTakenBy ?
-            qsTr("Taken by %1").arg(alreadyTakenBy) :
+            hasWhiteSpace ? qsTr("Alias cannot include spaces") :
+            alreadyTakenBy ? qsTr("Taken by %1").arg(alreadyTakenBy) :
             ""
 
         toolTip.text: qsTr(
@@ -263,7 +265,7 @@ HFlickableColumnPage {
 
         HTextField {
             width: parent.width
-            error: aliasField.alreadyTakenBy !== ""
+            error: aliasField.hasWhiteSpace || aliasField.alreadyTakenBy
             defaultText: aliasField.currentAlias
             placeholderText: qsTr("e.g. %1").arg((
                 nameField.item.text ||