anyrender_skia: size render_to_vec buffers before wrapping pixels (#49)

SkiaImageRenderer::render_to_vec currently assumes the caller has already
resized the Vec to the exact pixel buffer size. When callers pass an empty
Vec with only capacity reserved, wrap_pixels receives an empty slice and the
renderer panics.

Resize the Vec to image_info.compute_min_byte_size() before wrapping it so
offscreen rendering works with a plain empty Vec.

Author: jrmoulton

crates/anyrender_skia/src/image_renderer.rs

@@ -51,6 +51,8 @@ impl ImageRenderer for SkiaImageRenderer {
     ) {
         debug_timer!(timer, feature = "log_frame_times");
 
+        buffer.resize(self.image_info.compute_min_byte_size(), 0);
+
         let mut surface = surfaces::wrap_pixels(
             &self.image_info,
             &mut buffer[..],