Fix wave algorithm boundary conditions to prevent invalid alignments

[unavailable-2374]

Root cause analysis:

• Wave algorithm uses diagonal coordinate system where k = x - y
• For valid coordinates: x = (anti+k)/2 >= 0 and y = (anti-k)/2 >= 0
• This requires k to be in range [-anti, anti]
• Original code only checked hgh <= anti (y >= 0), not low >= -anti (x >= 0)

Fixes applied:

1. Entry point validation (Local_Alignment, Wrap_Around_Alignment, Find_Extension):

   • Add check: while (((anti+low)>>1) < 0) low += 1
   • Constrain minp to -anti (prevents wave expansion into x < 0 region)
   • Constrain maxp to anti (prevents wave expansion into y < 0 region)
   • Return error if no valid diagonals remain (low > hgh)

2. Internal bounds checking (all 6 wave functions):

   • Add check: if (x < 0 || x < k) mark diagonal as dead
   • Applied to both 0-wave initialization and main wave loops

3. Safety checks (forward_wave, reverse_wave):

   • Add check: if (avail == 0) return error
   • Catches case where all diagonals fail bounds checking

4. Early termination (all wave expansion loops):

   • Add check: if (hgh < low) break
   • Prevents infinite loops when all diagonals are trimmed

This multi-layer fix prevents invalid coordinates from being computed, rather than just detecting and skipping them after the fact.