Fix p11_error() implementation and test it

Author: MatthiasValvekens

extern/load_module.c

@@ -17,6 +17,9 @@ static PyObject* p11_error() {
                     NULL);
         PyObject* errmsg = PyUnicode_FromWideChar(msgbuffer, l);
         LocalFree(msgbuffer);
+        if (errmsg == NULL) {
+            Py_RETURN_NONE;
+        }
         return errmsg;
     } else {
         Py_RETURN_NONE;
@@ -61,7 +64,9 @@ static PyObject* p11_error() {
     }
     int len = strlen(error);
     PyObject* result = PyUnicode_DecodeUTF8(error, len, NULL);
-    PyMem_Free(error);
+    if (result == NULL) {
+        Py_RETURN_NONE;
+    }
     return result;
 }
 

tests/test_slots_and_tokens.py

@@ -14,6 +14,10 @@ def test_double_initialise(self):
         self.assertIsNotNone(pkcs11.lib(LIB))
         self.assertIsNotNone(pkcs11.lib(LIB))
 
+    def test_nonexistent_lib(self):
+        with self.assertRaises(RuntimeError):
+            pkcs11.lib("thislibdoesntexist.so")
+
     def test_double_initialise_different_libs(self):
         self.assertIsNotNone(pkcs11.lib(LIB))
         with self.assertRaises(pkcs11.AlreadyInitialized):