Merge pull request opencv#17841 from vpisarev:fixed_fs_dtor

* fixed issue opencv#17412

* Update test_io.cpp

Author: vpisarev

modules/core/src/persistence.cpp

@@ -1819,7 +1819,6 @@ void FileStorage::endWriteStruct()
 
 FileStorage::~FileStorage()
 {
-    p.release();
 }
 
 bool FileStorage::open(const String& filename, int flags, const String& encoding)

modules/core/test/test_io.cpp

@@ -1772,4 +1772,20 @@ TEST(Core_InputOutput, FileStorage_open_empty_16823)
     EXPECT_EQ(0, remove(fname.c_str()));
 }
 
+TEST(Core_InputOutput, FileStorage_copy_constructor_17412)
+{
+    std::string fname = tempfile("test.yml");
+    FileStorage fs_orig(fname, cv::FileStorage::WRITE);
+    fs_orig << "string" << "wat";
+    fs_orig.release();
+
+    // no crash anymore
+    cv::FileStorage fs;
+    fs = cv::FileStorage(fname,  cv::FileStorage::READ);
+    std::string s;
+    fs["string"] >> s;
+    EXPECT_EQ(s, "wat");
+    EXPECT_EQ(0, remove(fname.c_str()));
+}
+
 }} // namespace