decoder: Avoid unreachable code

If all the features are enabled, then the return statement
at the end of the function becomes unreachable code. Avoid it
by adding specific returns when certain paths are unavailable.

PiperOrigin-RevId: 679731916

src/decoder/mod.rs

@@ -79,31 +79,30 @@ impl CodecChoice {
         match self {
             CodecChoice::Auto => {
                 // Preferred order of codecs in Auto mode: Android MediaCodec, Dav1d, Libgav1.
-                return CodecChoice::MediaCodec
+                CodecChoice::MediaCodec
                     .get_codec()
                     .or_else(|_| CodecChoice::Dav1d.get_codec())
-                    .or_else(|_| CodecChoice::Libgav1.get_codec());
+                    .or_else(|_| CodecChoice::Libgav1.get_codec())
             }
             CodecChoice::Dav1d => {
                 #[cfg(feature = "dav1d")]
-                {
-                    return Ok(Box::<Dav1d>::default());
-                }
+                return Ok(Box::<Dav1d>::default());
+                #[cfg(not(feature = "dav1d"))]
+                return Err(AvifError::NoCodecAvailable);
             }
             CodecChoice::Libgav1 => {
                 #[cfg(feature = "libgav1")]
-                {
-                    return Ok(Box::<Libgav1>::default());
-                }
+                return Ok(Box::<Libgav1>::default());
+                #[cfg(not(feature = "libgav1"))]
+                return Err(AvifError::NoCodecAvailable);
             }
             CodecChoice::MediaCodec => {
                 #[cfg(feature = "android_mediacodec")]
-                {
-                    return Ok(Box::<MediaCodec>::default());
-                }
+                return Ok(Box::<MediaCodec>::default());
+                #[cfg(not(feature = "android_mediacodec"))]
+                return Err(AvifError::NoCodecAvailable);
             }
         }
-        Err(AvifError::NoCodecAvailable)
     }
 }