Add missing break in execution switch

The & command was mssing a break at its end.

starfish.js

@@ -312,6 +312,7 @@ class CodeBox {
                         this.stacks[this.curr_stack].Push(this.stacks[this.curr_stack].register);
                         this.stacks[this.curr_stack].register = null;
                     }
+                    break;
                 }
                 case ":":
                     this.stacks[this.curr_stack].Duplicate();