fix(gl): align glDrawBuffers indices with attachment points

GLES 3.0 strictly requires that the i-th buffer in `glDrawBuffers` corresponds to `GL_COLOR_ATTACHMENTi`.
This fixes a `GL_INVALID_OPERATION` (0x502) error by padding the draw buffers array with `GL_NONE` at index 0, ensuring `GL_COLOR_ATTACHMENT1` is correctly placed at index 1.

Author: mikai233

librashader-runtime-gl/src/gl/gl3/framebuffer.rs

@@ -131,7 +131,7 @@ impl FramebufferInterface for Gl3Framebuffer {
             );
 
             fb.ctx.read_buffer(glow::COLOR_ATTACHMENT0);
-            fb.ctx.draw_buffers(&[glow::COLOR_ATTACHMENT1]);
+            fb.ctx.draw_buffers(&[glow::NONE, glow::COLOR_ATTACHMENT1]);
 
             fb.ctx.blit_framebuffer(
                 0,