QDBusError: add assignment operator from QDBusMessage

There's an implicit constructor for this conversion,
so there should be an assignment operator, too,
as an optimisation.

Change-Id: I1d1646cbafdea5a4f80b11b011a8940b65a9fb9f
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/dbus/qdbuserror.cpp

@@ -302,6 +302,24 @@ QDBusError &QDBusError::operator=(const QDBusError &other)
     return *this;
 }
 
+/*!
+  \internal
+  Assignment operator from a QDBusMessage
+*/
+QDBusError &QDBusError::operator=(const QDBusMessage &qdmsg)
+{
+    if (qdmsg.type() == QDBusMessage::ErrorMessage) {
+        code = ::get(qdmsg.errorName().toUtf8().constData());
+        nm = qdmsg.errorName();
+        msg = qdmsg.errorMessage();
+    } else {
+        code =NoError;
+        nm.clear();
+        msg.clear();
+    }
+    return *this;
+}
+
 /*!
     Returns this error's ErrorType.
 

src/dbus/qdbuserror.h

@@ -98,6 +98,7 @@ public:
     QDBusError(ErrorType error, const QString &message);
     QDBusError(const QDBusError &other);
     QDBusError &operator=(const QDBusError &other);
+    QDBusError &operator=(const QDBusMessage &msg);
 
     ErrorType type() const;
     QString name() const;