Add virtual destructor

SquiLu/include/sqstdio.h

@@ -7,6 +7,7 @@
 //#define SQSTD_STREAM_TYPE_TAG 0x80000000
 
 struct SQStream {
+    virtual ~SQStream() {}
 	virtual SQInteger Read(void *buffer, SQInteger size) = 0;
 	virtual SQInteger Gets(char *buffer, SQInteger size) = 0;
 	virtual SQInteger Write(const void *buffer, SQInteger size) = 0;