Running total for a row avoiding NULL values

Does anyone know how to calculate running total for a row making sure null values are avoided? 

My example: 

Each row represents amount of shops someone has in the neighbourhood, and columns represent amount of shops visited.

E.g. 18 people have 7 shops in their neighbourhood. From which 11 people visited 0 shops and 2 people visited 1 shop, etc. 

I would like to get the running total of the row with fillowing result: 

In order to calculate running total for each visited shop, I used the following measure: 

Count of PersonId running total in VisitedShops = 
CALCULATE(
	DISTINCTCOUNT('MyData'[PersonId]),
	FILTER(
		ALLSELECTED('MyData'[VisitedShops]),
		ISONORAFTER('MyData'[VisitedShops], MIN('MyData'[VisistedShops]), ASC)
	)
)

This measure gives me the wrong result because it skips null values and starts calculating running totals all over again: 

Hope you are able to help! Thanks in advance!