[vulkan] Cope with an empty world model

Vulkan doesn't appreciate the empty buffers that result from the model
not having any textures or surfaces that can be rendered (rightfully so,
for such a bare-metal api).

libs/models/brush/vulkan_model_brush.c

@@ -303,7 +303,9 @@ Vulkan_Mod_ProcessTexture (model_t *mod, texture_t *tx, vulkan_ctx_t *ctx)
 		mod->data = mctx;
 
 		r_notexture_mip->render = &vulkan_notexture;
-		load_textures (mod, ctx);
+		if (mod->brush.numtextures) {
+			load_textures (mod, ctx);
+		}
 		return;
 	}
 

libs/video/renderer/vulkan/vulkan_bsp.c

@@ -413,6 +413,10 @@ Vulkan_BuildDisplayLists (model_t **models, int num_models, vulkan_ctx_t *ctx)
 	bsppoly_t  *poly;
 	mod_brush_t *brush;
 
+	if (!num_models) {
+		return;
+	}
+
 	// run through all surfaces, chaining them to their textures, thus
 	// effectively sorting the surfaces by texture (without worrying about
 	// surface order on the same texture chain).
@@ -1037,6 +1041,9 @@ Vulkan_DrawWorld (qfv_renderframe_t *rFrame)
 	bctx->color = 0;
 
 	R_VisitWorldNodes (brush, ctx);
+	if (!bctx->vertex_buffer) {
+		return;
+	}
 	if (r_drawentities) {
 		for (size_t i = 0; i < r_ent_queue->ent_queues[mod_brush].size; i++) {
 			entity_t   *ent = r_ent_queue->ent_queues[mod_brush].a[i];
@@ -1089,6 +1096,9 @@ Vulkan_Bsp_Flush (vulkan_ctx_t *ctx)
 	size_t      offset = bframe->index_offset;
 	size_t      size = bframe->index_count * sizeof (uint32_t);
 
+	if (!bframe->index_count) {
+		return;
+	}
 	offset &= ~atom_mask;
 	size = (size + atom_mask) & ~atom_mask;
 

libs/video/renderer/vulkan/vulkan_lighting.c

@@ -927,6 +927,10 @@ Vulkan_LoadLights (model_t *model, const char *entity_data, vulkan_ctx_t *ctx)
 	lightingctx_t *lctx = ctx->lighting_context;
 	plitem_t   *entities = 0;
 
+	if (!entity_data) {
+		return;
+	}
+
 	lctx->lights.size = 0;
 	lctx->lightleafs.size = 0;
 	lctx->lightmats.size = 0;
@@ -1006,11 +1010,13 @@ Vulkan_LoadLights (model_t *model, const char *entity_data, vulkan_ctx_t *ctx)
 		PL_Free (entities);
 	}
 	Sys_MaskPrintf (SYS_vulkan, "loaded %zd lights\n", lctx->lights.size);
-	build_shadow_maps (lctx, ctx);
-	create_light_matrices (lctx);
-	locate_lights (model, lctx);
-	for (size_t i = 0; i < lctx->lights.size; i++) {
-		dump_light (&lctx->lights.a[i], lctx->lightleafs.a[i],
-					lctx->lightmats.a[i]);
+	if (lctx->lights.size) {
+		build_shadow_maps (lctx, ctx);
+		create_light_matrices (lctx);
+		locate_lights (model, lctx);
+		for (size_t i = 0; i < lctx->lights.size; i++) {
+			dump_light (&lctx->lights.a[i], lctx->lightleafs.a[i],
+						lctx->lightmats.a[i]);
+		}
 	}
 }