Uninformative deployments() error when no accounts registered

[hadley]

i.e. when accounts() returns NULL

> rsconnect::deployments("tests/testthat/tutorials-inst/inst/tutorials/test-1/")
Error in if (nrow(matchingAccounts) == 0) next :
  argument is of length zero

(Sorry this isn't a reprex, but the code path causing the error in deployments() looks fairly straightforward. Alternatively, maybe accounts() should always return a data frame)