SUMIF attempts to access sum_range argument when it doesn't exist

[colbybhearn]

If SUMIF is called where

• range is a single cell, not a range.
• criteria is anything that the single cell will pass
• sum_range is not specified

then EPPlus throws System.ArgumentOutOfRangeException

Here's a test method that could be added to SumIfTests.cs

        [TestMethod]
        public void SumIfSingleCell()
        {
            _worksheet.Cells["A1"].Value = 20;
            _worksheet.Cells["A2"].Formula = "SUMIF(A1,\">0\")";
            _worksheet.Calculate();

            Assert.AreEqual(20d, _worksheet.Cells["A2"].Value);
        }

I'll try to whip up a PR with the simple fix I've made to SumIf.cs

[swmal]

Hi Colby,

I have added your unit test and your fix to SUMIF to the codebase. Will be included in the next version. Many thanks for your contribution.

/Mats