Fix OpenTTD#9588, 140a96b: [Squirrel] Reaching memory limit during sc…

…ript registration could prevent further script detections

Also the allocation triggering the limit was never freed.
And if the exception was thrown in a constructor using placement new, the pre-allocated was not freed either.

src/3rdparty/squirrel/squirrel/sqobject.h

@@ -62,6 +62,21 @@ struct SQRefCounted
 	SQUnsignedInteger _uiRef;
 	struct SQWeakRef *_weakref;
 	virtual void Release()=0;
+
+	/* Placement new/delete to prevent memory leaks if constructor throws an exception. */
+	inline void *operator new(size_t size, SQRefCounted *place)
+	{
+		place->size = size;
+		return place;
+	}
+
+	inline void operator delete(void *ptr, SQRefCounted *place)
+	{
+		SQ_FREE(ptr, place->size);
+	}
+
+private:
+	size_t size;
 };
 
 struct SQWeakRef : SQRefCounted

src/script/squirrel.cpp

@@ -67,7 +67,7 @@ struct ScriptAllocator {
 	 * @param requested_size The requested size that was requested to be allocated.
 	 * @param p              The pointer to the allocated object, or null if allocation failed.
 	 */
-	void CheckAllocation(size_t requested_size, const void *p)
+	void CheckAllocation(size_t requested_size, void *p)
 	{
 		if (this->allocated_size > this->allocation_limit && !this->error_thrown) {
 			/* Do not allow allocating more than the allocation limit, except when an error is
@@ -77,6 +77,11 @@ struct ScriptAllocator {
 			char buff[128];
 			seprintf(buff, lastof(buff), "Maximum memory allocation exceeded by " PRINTF_SIZE " bytes when allocating " PRINTF_SIZE " bytes",
 				this->allocated_size - this->allocation_limit, requested_size);
+			/* Don't leak the rejected allocation. */
+			free(p);
+			p = nullptr;
+			/* Allocation rejected, don't count it. */
+			this->allocated_size -= requested_size;
 			throw Script_FatalError(buff);
 		}
 
@@ -93,6 +98,8 @@ struct ScriptAllocator {
 			this->error_thrown = true;
 			char buff[64];
 			seprintf(buff, lastof(buff), "Out of memory. Cannot allocate " PRINTF_SIZE " bytes", requested_size);
+			/* Allocation failed, don't count it. */
+			this->allocated_size -= requested_size;
 			throw Script_FatalError(buff);
 		}
 	}
@@ -757,6 +764,11 @@ void Squirrel::Uninitialize()
 	/* Clean up the stuff */
 	sq_pop(this->vm, 1);
 	sq_close(this->vm);
+
+	assert(this->allocator->allocated_size == 0);
+
+	/* Reset memory allocation errors. */
+	this->allocator->error_thrown = false;
 }
 
 void Squirrel::Reset()