Add error_scope to py::class_::dealloc() to protect destructor calls (#2342)

Fixes issue #1878

tests/test_class.py

@@ -323,3 +323,9 @@ def test_non_final_final():
         class PyNonFinalFinalChild(m.IsNonFinalFinal):
             pass
     assert str(exc_info.value).endswith("is not an acceptable base type")
+
+
+# https://github.com/pybind/pybind11/issues/1878
+def test_exception_rvalue_abort():
+    with pytest.raises(RuntimeError):
+        m.PyPrintDestructor().throw_something()