Fix CSO file crash by initializing pointers and adding validation

[DocMAX]

This fix addresses a crash in the PCSX2 emulator when attempting to open CSO (Compressed ISO) files.

Root Cause

• Uninitialized m_src pointer in CsoFileReader constructor
• Invalid pointer handling in file operations
• Memory corruption when dereferencing invalid pointers

Solution

• Proper constructor initialization of all pointer members
• Added IsValidPointer() helper function for runtime validation
• Enhanced error handling throughout file operations
• Defensive programming to prevent crashes

Changes Made

1. pcsx2/CDVD/CsoFileReader.cpp:

   • Initialize all members in constructor
   • Add pointer validation helper function
   • Improve Open2() and Close2() methods

2. libretro/libretro-common/streams/file_stream.c:

   • Add safety checks in filestream_close()
   • Prevent crashes on invalid file handles

Impact

• Prevents crashes when opening CSO files
• Maintains all existing functionality
• Backward compatible
• Follows best practices for defensive programming

Testing

• All modified files compile successfully
• Changes are minimal and focused
• No breaking changes to existing functionality