test: allow mute state updates while audio subsystem is disabled

src/audio.rs

@@ -140,15 +140,14 @@ impl Audio {
     ///
     /// If audio is disabled, this function does nothing.
     pub fn set_mute(&mut self, mute: bool) {
-        if self.disabled {
-            return;
-        }
-
+        if !self.disabled {
             let channels = 4;
             let volume = if mute { 0 } else { 32 };
             for i in 0..channels {
                 mixer::Channel(i).set_volume(volume);
             }
+        }
+
         self.muted = mute;
     }