Fix issue with calling lstClear() twice.

The list pointer was not nulled out so calling lstClear() caused a double free.

This is not a production issue but was noticed in some upcoming test code.

src/common/type/list.c

@@ -66,6 +66,7 @@ lstClear(List *const this)
         }
         MEM_CONTEXT_END();
 
+        this->pub.list = NULL;
         this->pub.listSize = 0;
         this->listSizeMax = 0;
     }

test/src/module/common/typeListTest.c

@@ -38,6 +38,7 @@ testRun(void)
         TEST_RESULT_Z(logBuf, "{size: 1}", "check log");
 
         TEST_RESULT_VOID(lstClear(list), "clear list");
+        TEST_RESULT_VOID(lstClear(list), "clear list again to ensure everything was cleared correctly");
         TEST_RESULT_VOID(FUNCTION_LOG_OBJECT_FORMAT(list, lstToLog, logBuf, sizeof(logBuf)), "bufToLog");
         TEST_RESULT_Z(logBuf, "{size: 0}", "check log");