addNumfmt() in xmlStyle.go seems to be wrong

[martianwei]

The addNumfmt function verifies whether xNumFmt.NumFmtId is less than or equal to builtinNumFmtsCount. If this condition is met, the function will not add it.

However, since my numFmtId is 8, this function prevents me from retrieving the correct NumFmt for my cell.

I believe it would be more effective to check if xNumFmt.NumFmtId is included in builtInNumFmt

Could Anyone help me fix it?

Number_Currency.xlsx

[tealeg]

Fixed by #796.