fix: hold piece now correctly uses next piece preview on first hold

app/src/main/java/com/mintris/model/GameBoard.kt

@@ -97,8 +97,13 @@ class GameBoard(
         if (holdPiece == null) {
             // If no piece is held, hold current piece and spawn new one
             holdPiece = current
+            currentPiece = nextPiece
             spawnNextPiece()
-            spawnPiece()
+            // Reset position of new piece
+            currentPiece?.apply {
+                x = (width - getWidth()) / 2
+                y = 0
+            }
         } else {
             // Swap current piece with held piece
             currentPiece = holdPiece