Fix focus handling in diff editor

Task-number: QTCREATORBUG-12288
Change-Id: Ie5195fd3447bcedc4f7fd0515bedb524b5d96663
Reviewed-by: Orgad Shaneh <orgads@gmail.com>

src/plugins/diffeditor/diffeditor.cpp

@@ -611,6 +611,7 @@ void DiffEditor::showDiffEditor(QWidget *newEditor)
 
     writeCurrentDiffEditorSetting(m_currentEditor);
     updateDiffEditorSwitcher();
+    widget()->setFocusProxy(m_currentEditor);
 }
 
 QWidget *DiffEditor::readLegacyCurrentDiffEditorSetting()

src/plugins/diffeditor/sidebysidediffeditorwidget.cpp

@@ -836,6 +836,7 @@ SideBySideDiffEditorWidget::SideBySideDiffEditorWidget(QWidget *parent)
     QVBoxLayout *l = new QVBoxLayout(this);
     l->setMargin(0);
     l->addWidget(m_splitter);
+    setFocusProxy(m_rightEditor);
 
     clear(tr("No controller"));
 }