Added a more helpful error message when there is no current animation for the animation player

scene/animation/animation_player.cpp

@@ -1294,12 +1294,12 @@ bool AnimationPlayer::is_valid() const {
 }
 
 float AnimationPlayer::get_current_animation_position() const {
-	ERR_FAIL_COND_V(!playback.current.from, 0);
+	ERR_FAIL_COND_V_MSG(!playback.current.from, 0, "AnimationPlayer has no current animation");
 	return playback.current.pos;
 }
 
 float AnimationPlayer::get_current_animation_length() const {
-	ERR_FAIL_COND_V(!playback.current.from, 0);
+	ERR_FAIL_COND_V_MSG(!playback.current.from, 0, "AnimationPlayer has no current animation");
 	return playback.current.from->animation->get_length();
 }