add assertion for size > 0 in arenaAllocateBlock()

src/asset.cpp

@@ -64,6 +64,7 @@ arenaAllocateBlock(memory_arena* arena, size_t block_size)
 {
 	// TODO: resizable memory arena
 	assert(arenaGetFreeSize(arena) >= block_size);
+	assert(block_size > 0);
 	void* ret = arena->next_free;
 	arena->next_free = (uint8_t*) arena->next_free + block_size;
 	return ret;