修复了一些bug

DoRunner/DefineVariableRunner.cs

@@ -79,7 +79,7 @@ namespace Convention.RScript.Runner
                 if (varTypeName == "string")
                 {
                     varType = typeof(string);
-                    varDefaultValue = varInitExpression == null ? string.Empty : varInitExpression;
+                    varDefaultValue = varInitExpression == null ? string.Empty : varInitExpression.Trim('\"');
                 }
                 else if (varTypeName == "int")
                 {

DoRunner/ExitNamespaceRunner.cs

@@ -22,7 +22,14 @@ namespace Convention.RScript.Runner
             // 还原上层命名空间的变量
             foreach (var local in context.CurrentLocalSpaceVariableNames.Peek())
             {
-                parser.context.Variables[local] = context.Variables[local].data;
+                if (context.Variables.ContainsKey(local))
+                {
+                    parser.context.Variables[local] = context.Variables[local].data;
+                }
+                else
+                {
+                    parser.context.Variables.Remove(local);
+                }
             }
             context.CurrentLocalSpaceVariableNames.Pop();
             // 弹栈