enable setting row height on rows without cell values

Created originally on Bitbucket by Former user

Was already merged in Bitbucket before import, marked as merged by the import user

If a row does not have any cells with values, openpyxl fails to set the row height.

In this example only row 1 gets height 50:

from openpyxl import Workbook
wb = Workbook()
ws = wb.get_active_sheet()
ws.cell('A1').value = "test"
ws.row_dimensions[ws.cell('A1').row].height = 50
ws.row_dimensions[ws.cell('B2').row].height = 50
wb.save("test.xlsx")