Fix: Relocking min amount bypass (#575)

### Description

[Hats issue
#10](hats-finance#10)
identified that in the event of relocking a completed lock, there was no
minimum check that was present in a standard lock, this was given the
assumption that relocking would only occur on non expired locks.

contracts/governance/locking/LockingRelock.sol

@@ -26,6 +26,7 @@ abstract contract LockingRelock is LockingBase {
     uint32 newSlopePeriod,
     uint32 newCliff
   ) external returns (uint256) {
+    require(newAmount >= 1e18, "amount is less than minimum");
     require(newDelegate != address(0), "delegate is zero");
 
     address account = verifyLockOwner(id);
@@ -67,7 +68,6 @@ abstract contract LockingRelock is LockingBase {
     uint32 newCliff,
     uint32 toTime
   ) internal view {
-    require(newAmount > 0, "zero amount");
     require(newCliff <= MAX_CLIFF_PERIOD, "cliff too big");
     require(newSlopePeriod <= MAX_SLOPE_PERIOD, "slope period too big");
     require(newSlopePeriod > 0, "slope period equal 0");

test/unit/governance/Locking/relock.t.sol

@@ -230,7 +230,7 @@ contract Relock_LockingTest is LockingTest {
     lockId = locking.lock(alice, alice, 38e18, 4, 3);
     _incrementBlock(2 * weekInBlocks);
 
-    vm.expectRevert("zero amount");
+    vm.expectRevert("amount is less than minimum");
     vm.prank(alice);
     locking.relock(lockId, alice, 0, 5, 1);
   }
@@ -646,4 +646,29 @@ contract Relock_LockingTest is LockingTest {
     assertEq(mentoToken.balanceOf(bob), 100e18);
     assertEq(mentoToken.balanceOf(charlie), 100e18);
   }
+
+  function test_relock_whenAmountLessThanMinimum_shouldRevert() public {
+    mentoToken.mint(alice, 100e18);
+
+    vm.prank(alice);
+    lockId = locking.lock(alice, alice, 30e18, 3, 3);
+
+    _incrementBlock(6 * weekInBlocks);
+
+    vm.expectRevert("amount is less than minimum");
+    vm.prank(alice);
+    locking.relock(lockId, alice, 0.5e18, 3, 3);
+  }
+
+  function test_relock_whenAmountIsMinimum_shouldRelockSuccessfully() public {
+    mentoToken.mint(alice, 100e18);
+
+    vm.prank(alice);
+    lockId = locking.lock(alice, alice, 30e18, 3, 3);
+
+    _incrementBlock(6 * weekInBlocks);
+
+    vm.prank(alice);
+    locking.relock(lockId, alice, 1e18, 3, 3);
+  }
 }