Fix some unused variable warnings when asserts are disabled

src/core/serialisation.cpp

@@ -16,7 +16,7 @@
  * @param bytes_to_write The amount of bytes we want to try to write.
  * @return True iff the given amount of bytes can be written to the packet.
  */
-static bool BufferCanWriteToPacket(const std::vector<byte> &buffer, size_t limit, size_t bytes_to_write)
+[[maybe_unused]] static bool BufferCanWriteToPacket(const std::vector<byte> &buffer, size_t limit, size_t bytes_to_write)
 {
 	return buffer.size() + bytes_to_write <= limit;
 }

src/sl/extended_ver_sl.cpp

@@ -595,13 +595,13 @@ static void Save_SLXI()
 
 			if (extra_data_length > 0) {
 				SlWriteUint32(extra_data_length);
-				size_t written = SlGetBytesWritten();
+				[[maybe_unused]] size_t written = SlGetBytesWritten();
 				info->save_proc(info, false);
 				assert(SlGetBytesWritten() == written + extra_data_length);
 			}
 			if (chunk_count > 0) {
 				SlWriteUint32(chunk_count);
-				size_t written = SlGetBytesWritten();
+				[[maybe_unused]] size_t written = SlGetBytesWritten();
 				WriteChunkIdList(info->chunk_list, false);
 				assert(SlGetBytesWritten() == written + (chunk_count * 4));
 			}

src/spritecache.cpp

@@ -1135,11 +1135,11 @@ void *GetRawSprite(SpriteID sprite, SpriteType type, uint8 zoom_levels, Allocato
 
 		/* Load the sprite, if it is not loaded, yet */
 		if (sc->GetPtr() == nullptr) {
-			void *ptr = ReadSprite(sc, sprite, type, AllocSprite, nullptr, zoom_levels);
+			[[maybe_unused]] void *ptr = ReadSprite(sc, sprite, type, AllocSprite, nullptr, zoom_levels);
 			assert(ptr == _last_sprite_allocation.GetPtr());
 			sc->Assign(std::move(_last_sprite_allocation));
 		} else if ((sc->total_missing_zoom_levels & zoom_levels) != 0) {
-			void *ptr = ReadSprite(sc, sprite, type, AllocSprite, nullptr, sc->total_missing_zoom_levels & zoom_levels);
+			[[maybe_unused]] void *ptr = ReadSprite(sc, sprite, type, AllocSprite, nullptr, sc->total_missing_zoom_levels & zoom_levels);
 			assert(ptr == _last_sprite_allocation.GetPtr());
 			sc->Append(std::move(_last_sprite_allocation));
 		}

src/viewport.cpp

@@ -5601,8 +5601,8 @@ static void CheckOverflow(int &test, int &other, int max, int mult)
 	test = max;
 }
 
-static const uint X_DIRS = (1 << DIR_NE) | (1 << DIR_SW);
-static const uint Y_DIRS = (1 << DIR_SE) | (1 << DIR_NW);
+[[maybe_unused]] static const uint X_DIRS = (1 << DIR_NE) | (1 << DIR_SW);
+[[maybe_unused]] static const uint Y_DIRS = (1 << DIR_SE) | (1 << DIR_NW);
 static const uint HORZ_DIRS = (1 << DIR_W) | (1 << DIR_E);
 //static const uint VERT_DIRS = (1 << DIR_N) | (1 << DIR_S);