Remove redundant array access in Checkpoints (#5169)

contracts/utils/structs/Checkpoints.sol

@@ -142,7 +142,7 @@ library Checkpoints {
 
             // Update or push new checkpoint
             if (lastKey == key) {
-                _unsafeAccess(self, pos - 1)._value = value;
+                last._value = value;
             } else {
                 self.push(Checkpoint224({_key: key, _value: value}));
             }
@@ -337,7 +337,7 @@ library Checkpoints {
 
             // Update or push new checkpoint
             if (lastKey == key) {
-                _unsafeAccess(self, pos - 1)._value = value;
+                last._value = value;
             } else {
                 self.push(Checkpoint208({_key: key, _value: value}));
             }
@@ -532,7 +532,7 @@ library Checkpoints {
 
             // Update or push new checkpoint
             if (lastKey == key) {
-                _unsafeAccess(self, pos - 1)._value = value;
+                last._value = value;
             } else {
                 self.push(Checkpoint160({_key: key, _value: value}));
             }

scripts/generate/templates/Checkpoints.js

@@ -147,7 +147,7 @@ function _insert(${opts.checkpointTypeName}[] storage self, ${opts.keyTypeName}
 
         // Update or push new checkpoint
         if (lastKey == key) {
-            _unsafeAccess(self, pos - 1).${opts.valueFieldName} = value;
+            last.${opts.valueFieldName} = value;
         } else {
             self.push(${opts.checkpointTypeName}({${opts.keyFieldName}: key, ${opts.valueFieldName}: value}));
         }