refactor font loading

src/node_image_texture.cpp

@@ -18,8 +18,8 @@ void NodeImageTexture::clone_copy(Node* dest) const
 
 void NodeImageTexture::draw()
 {
-    tex.bind();
-    auto& sampler = tex.has_mips ? NodeImage::m_sampler_mips : NodeImage::m_sampler;
+    tex ? tex->bind() : glBindTexture(GL_TEXTURE_2D, 0);
+    auto& sampler = tex && tex->has_mips ? NodeImage::m_sampler_mips : NodeImage::m_sampler;
     sampler.bind(0);
     glEnable(GL_BLEND);
     ShaderManager::use(kShader::Texture);
@@ -27,6 +27,5 @@ void NodeImageTexture::draw()
     ShaderManager::u_mat4(kShaderUniform::MVP, m_mvp);
     NodeImage::m_plane.draw_fill();
     sampler.unbind();
-    tex.unbind();
     glDisable(GL_BLEND);
 }