fix(filters): prevent array out-of-bounds access

[Rushaway]

Description

This PR fixes potential array out-of-bounds access in the leader filter functions.
The issue occurred when trying to access g_iCurrentLeader array with client indices that could be larger than the array size.

Changes

• Added proper bounds checking in all filter functions:
  • Filter_Leaders
  • Filter_NotLeaders
  • Filter_Leader
  • Filter_NotLeader
• Standardized array bounds checking using MAXLEADER constant
• Improved safety by handling client indices >= MAXLEADER appropriately

Technical Details

• The g_iCurrentLeader array is sized to MAXLEADER
• Client indices can go up to MaxClients
• Added checks to prevent accessing the array with invalid indices
• For indices >= MAXLEADER, clients are considered "not leaders" by default

Testing

• Verified all filter functions work correctly with client indices
• Confirmed no array out-of-bounds errors occur
• Tested with various client indices including edge cases