DiffEditor: fix crash on diff action

Fix crash in GitClient::findExistingOrOpenNewDiffEditor as new DiffEditor
is not created

Change-Id: I7f0cd18ff3acffe1d83a5fad4d6f0df8c4d133f3
Reviewed-by: Eike Ziller <eike.ziller@digia.com>

src/plugins/diffeditor/diffeditorfile.cpp

@@ -49,7 +49,7 @@ DiffEditorFile::DiffEditorFile(const QString &mimeType, QObject *parent) :
 bool DiffEditorFile::setContents(const QByteArray &contents)
 {
     Q_UNUSED(contents);
-    return false;
+    return true;
 }
 
 void DiffEditorFile::setModified(bool modified)