:gear: Disable the remove button if slot is empty

dev-front/src/MechUtils.tsx

@@ -0,0 +1,5 @@
+import Mech from "./Mech";
+
+export function isEmptySlot(mech: Mech) {
+    return mech.id == null || mech.id < 0;
+}

dev-front/src/mech/squad/Member.tsx

@@ -1,6 +1,7 @@
 import React from 'react';
 import logo from '../../logo.svg';
 import Mech from '../../Mech';
+import { isEmptySlot } from '../../MechUtils'
 
 type MemberProps = {
     mech: Mech;
@@ -18,7 +19,7 @@ function Member({mech, remover} : MemberProps) {
                     <li>Health : {mech.health}</li>
                 </ul>
             </div>
-            <button onClick={event => remover()}>Remove</button>
+            <button onClick={event => remover()} disabled={isEmptySlot(mech)}>Remove</button>
         </div>
     )
 }