syncevo-dbus-server: fixed compile error

syncevo-dbus-server provides a logger which cannot be used after forking.
Declare that by adding the isProcessSafe() method.

src/syncevo-dbus-server.cpp

@@ -1394,6 +1394,8 @@ public:
                           const char *function,
                           const char *format,
                           va_list args);
+
+    virtual bool isProcessSafe() const { return false; }
 };
 
 /**