Fix DirectoryScanner implementation bugs

Fixed several bugs in the DirectoryScanner implementation:

Windows fixes:
- Fixed snprintf call missing buffer size parameter
- Fixed FindFirstFileA to use pattern (with wildcard) instead of path
- Changed sys_GetLastError() to GetLastError()
- Added scanner->first = false after using first result
- Removed TODO comment from cFileName usage (it's the correct field)

Linux fixes:
- Fixed typo: sys_reddir → sys_readdir
- Added missing 'done' field to DirectoryScanner struct
- Initialize scanner->done = false on successful opendir
- Fixed return value when scanner->done (should return 1, not -1)

src/file_system.h

@@ -18,6 +18,7 @@ typedef struct {
 typedef struct {
     DIR *d;
     struct dirent *e;
+    bool done;
 } DirectoryScanner;
 #endif