fix subtract with overflow in relative_min_window_density() consensus.rs

Panic with message: `Subtract with overflow`
at core/src/consensus.rs:78:27

When debug vars:
max_slot: 98879
global_slot + 1: 98880

Author: olton

core/src/consensus.rs

@@ -75,7 +75,7 @@ pub fn relative_min_window_density(b1: &MinaConsensusState, b2: &MinaConsensusSt
 
     let projected_window = {
         // Compute shift count
-        let shift_count = (max_slot - global_slot(b1) - 1).clamp(0, SUB_WINDOWS_PER_WINDOW);
+        let shift_count = (max_slot.wrapping_sub(global_slot(b1) + 1)).clamp(0, SUB_WINDOWS_PER_WINDOW);
 
         // Initialize projected window
         let mut projected_window = b1