Fix heap-buffer-overflow in ps_mllr_read

[lenzo-ka]

Description

Fixes a heap-buffer-overflow that occurs during error cleanup when reading malformed MLLR files.

The issue was caused by missing validation of dimension parameters. When n_feat or veclen[i] contained invalid values (zero, negative, or extremely large), ckd_calloc_3d would create corrupted array structures. During cleanup, ckd_free_3d would then read invalid metadata causing a heap-buffer-overflow.

Changes:

• Added validation to ensure n_feat is positive (line 70)
• Added validation to ensure veclen[i] is positive for each feature (line 82)

Verification steps

• Compiled successfully with no errors
• Prevents heap-buffer-overflow during cleanup with malformed input
• Matches existing validation pattern used for n_class (line 64)

Fixes #433