vello_hybrid: alloc only once for sizing the alpha texture buffer

sparse_strips/vello_hybrid/src/render.rs

diff --git a/sparse_strips/vello_hybrid/src/render.rs b/sparse_strips/vello_hybrid/src/render.rs
index 488524d..1d0226b 100644
--- a/sparse_strips/vello_hybrid/src/render.rs
+++ b/sparse_strips/vello_hybrid/src/render.rs
@@ -333,8 +333,10 @@
             render_data.alphas.len() <= (texture_width * texture_height * 16) as usize,
             "Alpha texture dimensions are too small to fit the alpha data"
         );
-        let mut alpha_data = render_data.alphas.clone();
-        alpha_data.resize((texture_width * texture_height * 16) as usize, 0);
+        let alpha_data_len = (texture_width * texture_height * 16) as usize;
+        let mut alpha_data = Vec::with_capacity(alpha_data_len);
+        alpha_data.extend_from_slice(&render_data.alphas);
+        alpha_data.resize(alpha_data_len, 0);
 
         queue.write_texture(
             wgpu::TexelCopyTextureInfo {