LibJS: Mark FinishUnwind as a terminator

Author: https://github.com/Hendiadyoin1
Commit: 6998b72d22
Pull-request: https://github.com/SerenityOS/serenity/pull/15971
Reviewed-by: https://github.com/FireFox317
Reviewed-by: https://github.com/alimpfard
Reviewed-by: https://github.com/kleinesfilmroellchen ✅

Userland/Libraries/LibJS/Bytecode/Op.h

@@ -783,6 +783,8 @@ public:
 
 class FinishUnwind final : public Instruction {
 public:
+    constexpr static bool IsTerminator = true;
+
     FinishUnwind(Label next)
         : Instruction(Type::FinishUnwind)
         , m_next_target(move(next))