Fix panic when minimizing, show backtraces when panicking

Former-commit-id: 0ad401d81a2f7b4d0b766578238d2ab9259f80eb

voxygen/src/main.rs

@@ -99,6 +99,7 @@ fn main() {
 
     // Set up panic handler to relay swish panic messages to the user
     let settings_clone = settings.clone();
+    let default_hook = panic::take_hook();
     panic::set_hook(Box::new(move |panic_info| {
         let msg = format!(" \
 A critical error has occured and Voxygen has been forced to terminate in an unusual manner. Details about the error can be found below.
@@ -126,6 +127,8 @@ The information below is intended for developers and testers.
         log::error!("VOXYGEN HAS PANICKED\n\n{}", msg);
 
         msgbox::create("Voxygen has panicked", &msg, msgbox::IconType::ERROR);
+
+        default_hook(panic_info);
     }));
 
     let mut global_state = GlobalState { settings, window };

voxygen/src/ui/mod.rs

@@ -609,8 +609,13 @@ impl Ui {
                 self.scale.window_resized(new_dims, renderer);
                 let (w, h) = self.scale.scaled_window_size().into_tuple();
                 self.ui.handle_event(Input::Resize(w, h));
-                self.cache
-                    .clear_graphic_cache(renderer, renderer.get_resolution().map(|e| e * 4));
+
+                let res = renderer.get_resolution();
+                // Avoid panic in graphic cache when minimizing
+                if res.x > 0 && res.y > 0 {
+                    self.cache
+                        .clear_graphic_cache(renderer, renderer.get_resolution().map(|e| e * 4));
+                }
                 // TODO: probably need to resize glyph cache, see conrod's gfx backend for reference
             }
         }