Fix crash when removing a folder

The problem is that the module_property of csync are not really tight to
a context, but are global to all the contextes.
Which means csync_owncloud may still have a pointer to the destroyed
context of the destroyed folder.
By always resetting the context pointer, we make sure there is no stale
pointers there

src/mirall/csyncthread.cpp

@@ -315,6 +315,7 @@ void CSyncThread::startSync()
     // cleans up behind us and emits finished() to ease error handling
     CSyncRunScopeHelper helper(_csync_ctx, this);
 
+    csync_set_module_property(_csync_ctx, "csync_context", _csync_ctx);
     csync_set_userdata(_csync_ctx, this);
 
     // csync_set_auth_callback( _csync_ctx, getauth );