fix potential fatal errors

src/coders/vec3.cpp

@@ -133,6 +133,9 @@ static model::Mesh load_mesh(
     if (flags == FLAG_ZLIB) {
         throw std::runtime_error("compression is not supported yet");
     }
+    if (attributeCount <= 0) {
+        throw std::runtime_error("mesh must have at least one attribute");
+    }
     std::vector<VertexAttribute> attributes;
     for (int i = 0; i < attributeCount; i++) {
         attributes.push_back(load_attribute(reader));

src/io/io.cpp

@@ -152,6 +152,9 @@ std::vector<ubyte> io::read_bytes(const path& filename) {
 std::string io::read_string(const path& filename) {
     size_t size;
     auto bytes = read_bytes(filename, size);
+    if (bytes == nullptr) {
+        throw std::runtime_error("could not read file " + filename.string());
+    }
     return std::string((const char*)bytes.get(), size);
 }
 

src/logic/scripting/lua/libs/libnetwork.cpp

@@ -266,8 +266,10 @@ static int l_peek(lua::State* L, network::Network& network) {
 static int l_available(lua::State* L, network::Network& network) {
     u64id_t id = lua::tointeger(L, 1);
 
-    if (auto connection = network.getConnection(id, false)) {
-        return lua::pushinteger(L, dynamic_cast<network::TcpConnection*>(connection)->available());
+    if (auto connection = dynamic_cast<network::ReadableConnection*>(
+            network.getConnection(id, false)
+        )) {
+        return lua::pushinteger(L, connection->available());
     }
 
     return 0;