[niepce] rust: Fix result warnings on Cairo

[Hubert Figuière <hub src gnome org>]

commit 2e8a76ce400cb7337b03bef60a2284612dcb9404
Author: Hubert Figuière <hub figuiere net>
Date:   Fri Jul 2 18:46:22 2021 -0400

    rust: Fix result warnings on Cairo
    
    - Added on_err_out!() macro

 crates/npc-fwk/src/base/debug.rs                   | 15 +++++++++++++++
 crates/npc-fwk/src/toolkit/widgets/rating_label.rs |  2 +-
 niepce-main/src/niepce/ui/library_cell_renderer.rs | 14 +++++++-------
 3 files changed, 23 insertions(+), 8 deletions(-)
---
diff --git a/crates/npc-fwk/src/base/debug.rs b/crates/npc-fwk/src/base/debug.rs
index 7c13775..d25fa73 100644
--- a/crates/npc-fwk/src/base/debug.rs
+++ b/crates/npc-fwk/src/base/debug.rs
@@ -1,3 +1,18 @@
+#[macro_export]
+macro_rules! on_err_out {
+    ($e:expr) => {
+        if let Err(err) = $e {
+            err_out!(
+                "{}:{} Error '{}': {}",
+                file!(),
+                line!(),
+                stringify!($e),
+                err
+            );
+        }
+    };
+}
+
 #[macro_export]
 macro_rules! dbg_out {
     ( $( $x:expr ),* ) => {
diff --git a/crates/npc-fwk/src/toolkit/widgets/rating_label.rs 
b/crates/npc-fwk/src/toolkit/widgets/rating_label.rs
index 7f445ab..88b03ca 100644
--- a/crates/npc-fwk/src/toolkit/widgets/rating_label.rs
+++ b/crates/npc-fwk/src/toolkit/widgets/rating_label.rs
@@ -197,7 +197,7 @@ impl RatingLabel {
             } else {
                 cr.set_source_pixbuf(unstar, x, y);
             }
-            cr.paint();
+            on_err_out!(cr.paint());
             x += w as f64;
         }
     }
diff --git a/niepce-main/src/niepce/ui/library_cell_renderer.rs 
b/niepce-main/src/niepce/ui/library_cell_renderer.rs
index c964146..74c4cd9 100644
--- a/niepce-main/src/niepce/ui/library_cell_renderer.rs
+++ b/niepce-main/src/niepce/ui/library_cell_renderer.rs
@@ -228,10 +228,10 @@ impl LibraryCellRendererPriv {
 
         cr.set_source_rgb(1.0, 1.0, 1.0);
         cr.rectangle(x, y, w.into(), h.into());
-        cr.stroke();
+        on_err_out!(cr.stroke());
 
         cr.set_source_pixbuf(&pixbuf, x, y);
-        cr.paint();
+        on_err_out!(cr.paint());
     }
 
     fn do_draw_flag(cr: &cairo::Context, flag: i32, r: &gdk::Rectangle) {
@@ -248,7 +248,7 @@ impl LibraryCellRendererPriv {
         let x: f64 = (r.x + r.width - CELL_PADDING - w).into();
         let y: f64 = (r.y + CELL_PADDING).into();
         cr.set_source_pixbuf(&pixbuf, x, y);
-        cr.paint();
+        on_err_out!(cr.paint());
     }
 
     fn do_draw_status(cr: &cairo::Context, status: FileStatus, r: &gdk::Rectangle) {
@@ -258,7 +258,7 @@ impl LibraryCellRendererPriv {
         let x: f64 = (r.x + CELL_PADDING).into();
         let y: f64 = (r.y + CELL_PADDING).into();
         cr.set_source_pixbuf(&EMBLEMS.status_missing, x, y);
-        cr.paint();
+        on_err_out!(cr.paint());
     }
 
     fn do_draw_format_emblem(cr: &cairo::Context, emblem: &Pixbuf, r: &gdk::Rectangle) -> i32 {
@@ -268,7 +268,7 @@ impl LibraryCellRendererPriv {
         let x: f64 = (r.x + r.width - left).into();
         let y: f64 = (r.y + r.height - CELL_PADDING - h).into();
         cr.set_source_pixbuf(emblem, x, y);
-        cr.paint();
+        on_err_out!(cr.paint());
         left
     }
 
@@ -279,11 +279,11 @@ impl LibraryCellRendererPriv {
 
         cr.rectangle(x, y, LABEL_SIZE.into(), LABEL_SIZE.into());
         cr.set_source_rgb(1.0, 1.0, 1.0);
-        cr.stroke();
+        on_err_out!(cr.stroke());
         cr.rectangle(x, y, LABEL_SIZE.into(), LABEL_SIZE.into());
         let rgb: gdk::RGBA = colour.into();
         cr.set_source_rgba(rgb.red, rgb.green, rgb.blue, rgb.alpha);
-        cr.fill();
+        on_err_out!(cr.fill());
     }
 
     fn get_colour(&self, label_id: i32) -> Option<RgbColour> {