stream: fix buffered_sys and cached_file destruction

We had to introduce out-of-order construction for those classes, but we
forgot to implement out-of-order destruction. File gets closed first
by cached_file::m_source destructor, then inherited destructor
cache::~cache() which flushes the cache is called.

Signed-off-by: Simon Rozman <simon@rozman.si>

include/stdex/stream.hpp

@@ -858,6 +858,11 @@ namespace stdex
 				m_source = &source;
 			}
 
+			void done()
+			{
+				m_source = nullptr;
+			}
+
 		public:
 			converter(_Inout_ basic& source) :
 				basic(source.state()),
@@ -1215,6 +1220,13 @@ namespace stdex
 				m_write_buffer(write_buffer_size)
 			{}
 
+			void done()
+			{
+				if (m_source)
+					flush_write();
+				converter::done();
+			}
+
 		public:
 			buffer(_Inout_ basic& source, _In_ size_t read_buffer_size = default_buffer_size, _In_ size_t write_buffer_size = default_buffer_size) :
 				converter(source),
@@ -1651,6 +1663,17 @@ namespace stdex
 #endif
 			}
 
+			void done()
+			{
+				if (m_source) {
+					flush_cache();
+					if (!ok()) _Unlikely_
+						throw std::runtime_error("cache flush failed"); // Data loss occured
+					m_source->seek(m_offset);
+					m_source = nullptr;
+				}
+			}
+
 		public:
 			cache(_Inout_ basic_file& source, _In_ size_t cache_size = default_cache_size) :
 				basic(source.state()),
@@ -2135,6 +2158,11 @@ namespace stdex
 				init(m_source);
 			}
 
+			virtual ~buffered_sys()
+			{
+				done();
+			}
+
 		protected:
 			basic_sys m_source;
 		};
@@ -2697,6 +2725,11 @@ namespace stdex
 				init(m_source);
 			}
 
+			virtual ~cached_file()
+			{
+				done();
+			}
+
 			///
 			/// Opens file
 			///