debugger: move spacer in "Start External" dialog to a better place

src/plugins/debugger/startexternaldialog.ui

@@ -20,19 +20,6 @@
    <property name="margin">
     <number>9</number>
    </property>
-   <item>
-    <spacer>
-     <property name="orientation">
-      <enum>Qt::Vertical</enum>
-     </property>
-     <property name="sizeHint" stdset="0">
-      <size>
-       <width>407</width>
-       <height>16</height>
-      </size>
-     </property>
-    </spacer>
-   </item>
    <item>
     <layout class="QGridLayout">
      <property name="margin">
@@ -87,6 +74,19 @@
      </item>
     </layout>
    </item>
+   <item>
+    <spacer>
+     <property name="orientation">
+      <enum>Qt::Vertical</enum>
+     </property>
+     <property name="sizeHint" stdset="0">
+      <size>
+       <width>407</width>
+       <height>16</height>
+      </size>
+     </property>
+    </spacer>
+   </item>
    <item>
     <widget class="Line" name="line">
      <property name="orientation">