Some minor code cleanups

src/client/content_mapblock.cpp

@@ -103,7 +103,7 @@ void MapblockMeshGenerator::getSpecialTile(int index, TileSpec *tile_ret, bool a
 
 	for (auto &layernum : tile_ret->layers) {
 		TileLayer *layer = &layernum;
-		if (layer->texture_id == 0)
+		if (layer->empty())
 			continue;
 		top_layer = layer;
 		if (!layer->has_color)

src/client/mapblock_mesh.cpp

@@ -347,7 +347,7 @@ void getNodeTileN(MapNode mn, const v3s16 &p, u8 tileindex, MeshMakeData *data,
 	tile = f.tiles[tileindex];
 	bool has_crack = p == data->m_crack_pos_relative;
 	for (TileLayer &layer : tile.layers) {
-		if (layer.texture_id == 0)
+		if (layer.empty())
 			continue;
 		if (!layer.has_color)
 			mn.getColor(f, &(layer.color));

src/client/meshgen/collector.cpp

@@ -12,7 +12,7 @@ void MeshCollector::append(const TileSpec &tile, const video::S3DVertex *vertice
 {
 	for (int layernum = 0; layernum < MAX_TILE_LAYERS; layernum++) {
 		const TileLayer *layer = &tile.layers[layernum];
-		if (layer->texture_id == 0)
+		if (layer->empty())
 			continue;
 		append(*layer, vertices, numVertices, indices, numIndices, layernum,
 				tile.world_aligned);

src/irrlicht_changes/CGUITTFont.cpp

@@ -897,6 +897,8 @@ video::IImage* CGUITTFont::createTextureFromChar(const char32_t& ch)
 
 	// Acquire a read-only lock of the corresponding page texture.
 	void* ptr = tex->lock(video::ETLM_READ_ONLY);
+	if (!ptr)
+		return nullptr;
 
 	video::ECOLOR_FORMAT format = tex->getColorFormat();
 	core::dimension2du tex_size = tex->getOriginalSize();

src/irrlicht_changes/CGUITTFont.h

@@ -200,9 +200,13 @@ namespace gui
 			//! Updates the texture atlas with new glyphs.
 			void updateTexture()
 			{
-				if (!dirty) return;
+				if (!dirty)
+					return;
 
 				void* ptr = texture->lock();
+				if (!ptr)
+					return;
+
 				video::ECOLOR_FORMAT format = texture->getColorFormat();
 				core::dimension2du size = texture->getOriginalSize();
 				video::IImage* pageholder = driver->createImageFromData(format, size, ptr, true, false);