window: Adjust to image size when opening

Give LpImage a native with that should feel nice.
When opening a new window with a new image the window size
is determined by LpImage's natural width.
The image size and EXIF data is loaded before the image such
that the window can be shown in the right dimension while
loading the actual image.

src/util.rs

@@ -5,7 +5,7 @@ use glib::translate::*;
 
 use anyhow::Context;
 
-use std::fmt::Write;
+use std::fmt::{Debug, Write};
 
 pub fn utf8_collate_key_for_filename(filename: &str) -> String {
     unsafe {
@@ -62,3 +62,15 @@ pub fn compare_by_name(file_a: &gio::File, file_b: &gio::File) -> std::cmp::Orde
 
     utf8_collate_key_for_filename(&name_a).cmp(&utf8_collate_key_for_filename(&name_b))
 }
+
+pub async fn spawn<T: Debug + Send + 'static>(
+    name: &str,
+    f: impl Fn() -> T + Send + 'static,
+) -> async_std::io::Result<T> {
+    log::trace!("Starting thread '{name}'");
+
+    Ok(async_std::task::Builder::new()
+        .name(name.to_string())
+        .spawn(async_global_executor::spawn_blocking(f))?
+        .await)
+}