Fix idm remove

idm remove calls shared_ptr::exchange with a null_ptr.
This calls the stored object's constructor with null args.
Let's just add an exchange overload for null_ptr

rpcs3/Emu/NP/np_contexts.cpp

@@ -238,7 +238,7 @@ matching_ctx::matching_ctx(vm::ptr<SceNpId> npId, vm::ptr<SceNpMatchingHandler>
 	this->handler = handler;
 	this->arg = arg;
 }
-void matching_ctx::queue_callback(u32 req_id, s32 event, s32 error_code)
+void matching_ctx::queue_callback(u32 req_id, s32 event, s32 error_code) const
 {
 	if (handler)
 	{
@@ -249,7 +249,7 @@ void matching_ctx::queue_callback(u32 req_id, s32 event, s32 error_code)
 			});
 	}
 }
-void matching_ctx::queue_gui_callback(s32 event, s32 error_code)
+void matching_ctx::queue_gui_callback(s32 event, s32 error_code) const
 {
 	if (gui_handler)
 	{

rpcs3/Emu/NP/np_contexts.h

@@ -289,8 +289,8 @@ struct matching_ctx
 {
 	matching_ctx(vm::ptr<SceNpId> npid, vm::ptr<SceNpMatchingHandler> handler, vm::ptr<void> arg);
 
-	void queue_callback(u32 req_id, s32 event, s32 error_code);
-	void queue_gui_callback(s32 event, s32 error_code);
+	void queue_callback(u32 req_id, s32 event, s32 error_code) const;
+	void queue_gui_callback(s32 event, s32 error_code) const;
 
 	static const u32 id_base = 0x9001;
 	static const u32 id_step = 1;

rpcs3/util/shared_ptr.hpp

@@ -895,6 +895,17 @@ namespace stx
 			return value;
 		}
 
+		[[nodiscard]] shared_type exchange(struct null_ptr_t) noexcept
+		{
+			atomic_ptr old;
+			old.m_val.raw() = m_val.exchange(0);
+			old.m_val.raw() += 1;
+
+			shared_type result;
+			result.m_ptr = std::launder(ptr_to(old.m_val));
+			return result;
+		}
+
 		// Ineffective
 		[[nodiscard]] bool compare_exchange(shared_type& cmp_and_old, shared_type exch)
 		{