Use dedicated constants for unknown image dimensions in ImageStrategy

Author: TobiGr

app/src/main/java/org/schabi/newpipe/util/image/ImageStrategy.kt

@@ -186,7 +186,8 @@ object ImageStrategy {
     fun dbUrlToImageList(url: String?): List<Image> {
         return when (url) {
             null -> listOf()
-            else -> listOf(Image(url, -1, -1, ResolutionLevel.UNKNOWN))
+            else -> listOf(Image(url, Image.HEIGHT_UNKNOWN, Image.WIDTH_UNKNOWN,
+                ResolutionLevel.UNKNOWN))
         }
     }
 }