exclude C source files from non-darwin targets

backend/app.go

@@ -235,10 +235,12 @@ func (a *App) setupMPRIS(mprisAppName string) {
 
 func (a *App) setupMPMedia() {
 	a.MPMediaHandler = NewMPMediaHandler(a.Player, a.PlaybackManager)
-	a.MPMediaHandler.ArtURLLookup = func(coverID string) (string, error) {
-		// artwork needs to be in cache before playback, so cover is retrieved in advance.
-		a.ImageManager.GetCoverThumbnail(coverID)
-		return a.ImageManager.GetCoverArtUrl(coverID)
+	if a.MPMediaHandler != nil {
+		a.MPMediaHandler.ArtURLLookup = func(coverID string) (string, error) {
+			// artwork needs to be in cache before playback, so cover is retrieved in advance.
+			a.ImageManager.GetCoverThumbnail(coverID)
+			return a.ImageManager.GetCoverArtUrl(coverID)
+		}
 	}
 }
 

backend/mpmediabridge.h

@@ -1,3 +1,5 @@
+//go:build darwin
+
 /**
  * mpmediabridge.h
  * 

backend/mpmediabridge.m

@@ -1,3 +1,5 @@
+//go:build darwin
+
 #import "mpmediabridge.h"
 
 /**