Attrition is ordered alphabetically in plots (diagram)

When I use the package CohortCharacteristics the attrition is ordered alphabetically in plots (this does not happen in tables) instead of following the order of the results

```
library(CohortCharacteristics)

cdm <- mockCohortCharacteristics()

# attrition of cohort 2
result2 <- summariseCohortAttrition(cdm$cohort1, cohortId = 2)

# attrition of cohort 1
result1 <- summariseCohortAttrition(cdm$cohort1, cohortId = 1)

# bind results (cohort 2 is before cohort 1)
result <- bind(result2, result1)

# table works
tableCohortAttrition(result)

# plot recorders
plotCohortAttrition(result, type = "png")
```

Start by running the reproducible example with mockCohortCharacteristics(), summariseCohortAttrition(), bind(), tableCohortAttrition(), and plotCohortAttrition(). Compare the plot's attrition ordering with the bound result and the table output. Done means plotCohortAttrition preserves the input result order, including cohort 2 before cohort 1.

Written by the indexing model from the issue text.