UI: Clean up toolbar form markup

UI/forms/source-toolbar/game-capture-toolbar.ui

@@ -148,7 +148,7 @@
     </widget>
    </item>
    <item>
-    <widget class="QWidget" name="empty">
+    <widget class="QFrame" name="empty">
      <property name="sizePolicy">
       <sizepolicy hsizetype="Expanding" vsizetype="Preferred">
        <horstretch>0</horstretch>

UI/forms/source-toolbar/text-source-toolbar.ui

@@ -83,7 +83,7 @@
     </widget>
    </item>
    <item>
-    <widget class="QWidget" name="emptySpace">
+    <widget class="QFrame" name="emptySpace">
      <property name="sizePolicy">
       <sizepolicy hsizetype="Expanding" vsizetype="Preferred">
        <horstretch>0</horstretch>