Initialize Interface factory pointer to fix Coverity warning.

Coverity complains (in CID 1335150) about `Generator::parseInterface()`
since the default copy-ctor for `Interface` will end up copying
uninitialized memory (the unset `m_factory` member). Fixed by
initializing the m_factory.

REVIEW:127836

src/wayland/tools/generator.cpp

@@ -208,6 +208,7 @@ Interface::Interface() = default;
 Interface::Interface(const QXmlStreamAttributes &attributes)
     : m_name(attributes.value(QStringLiteral("name")).toString())
     , m_version(attributes.value(QStringLiteral("version")).toUInt())
+    , m_factory(Q_NULLPTR)
 {
     auto it = s_clientClassNameMapping.constFind(m_name);
     if (it != s_clientClassNameMapping.constEnd()) {