fix NTFS index record processing

[NBojic]

Proposed fix for NTFS index entry processing in function "ntfs_dir_open_meta", fixes #2735.

• Function "ntfs_dir_open_meta" now checks for each index record whether it is active or not by reading the bitmap attribute. "ntfs_dir_open_meta" scans a big buffer from start to end in a for-loop and looks for index records. The fix uses the current parsing offset from the big for-loop to find out which bit of the bitmap is associated with the index record.
• "ntfs_dir_open_meta" calls function "ntfs_proc_idxentry" to process an index entry. "ntfs_proc_idxentry" takes argument "a_is_del". The fix sets "a_is_del" to 1 if the current index entry corresponds to an inactive index record.