Skip blank cells in a loop

I am converting an inventory from the form:

Item ID	#Small	#Medium	#Large...
1	4	5	6
2	8	9	10

to

Item ID/SIZE	#Available
1Small	4
1Medium	5
1Large	6
2Small	8
...

I have code that does this effectively.

Dim sizes As Integer
sizes = WorksheetFunction.CountA(Range("1:1")) - 1

Do While ActiveCell.Value <> ""
    
    For i = 1 To sizes
        ActiveCell.Offset(1, 0).EntireRow.Insert
        ActiveCell.Offset(1, 0).Select
        ActiveCell.Value = ActiveCell.Offset(-i, 0).Value & Cells(1, i + 1).Value
        ActiveCell.Offset(0, 1).Value = ActiveCell.Offset(-i, i).Value
    Next i

ActiveCell.Offset(-sizes, 0).EntireRow.Delete

Loop

However, if there are blanks in the table, my current code creates items with 0 available. I would like it to skip blanks and only create a new item if there is a non-zero quantity of that size for that item.