idb-import plugin causes memory leak

[xusheng6]

idb-import plugin is causing memory leak on BinaryNinjaCore::BinaryView object. I put a breakpoint on the dtor BinaryView::~BinaryView(), and I close the last tab of a binary. If the idb-import plugin is enabled, then the dtor is not called; if I disable the idb-import plugin, then the dtor gets called as expected. It seems like the plugin is causing a memory leak. I am not sure whether this is caused by the plugin itself, or the rust binding.