Error on missing Codec changed to "Unable to Play"

The error message was harsh, and new users might close the software
imediatly after it fails.

src/renderer/pages/player-page.js

@@ -303,7 +303,7 @@ function renderCastScreen (state) {
     isCast = false
   } else if (state.playing.location === 'error') {
     castIcon = 'error_outline'
-    castType = 'Error'
+    castType = 'Unable to Play'
     isCast = false
   }