Truncate webgl luts like wgpu

sparse_strips/vello_hybrid/src/render/webgl.rs

diff --git a/sparse_strips/vello_hybrid/src/render/webgl.rs b/sparse_strips/vello_hybrid/src/render/webgl.rs
index 7cbba00..a6cf398 100644
--- a/sparse_strips/vello_hybrid/src/render/webgl.rs
+++ b/sparse_strips/vello_hybrid/src/render/webgl.rs
@@ -1539,6 +1539,7 @@
 
         // Take ownership of the luts to avoid copying, then resize for texture padding.
         let mut luts = gradient_cache.take_luts();
+        let old_luts_len = luts.len();
         luts.resize(total_capacity, 0);
 
         gl.active_texture(WebGl2RenderingContext::TEXTURE0);
@@ -1560,7 +1561,8 @@
         )
         .unwrap();
 
-        // Restore the luts back to the cache.
+        // Restore the luts back to the cache
+        luts.truncate(old_luts_len);
         gradient_cache.restore_luts(luts);
     }