[Rd] Argument names for rgb() only applied for alpha given (PR#9118)

[stefan.albrecht at allianz.com]

Full_Name: Stefan Albrecht
Version: 2.3.1
OS: Windows XP
Submission from: (NULL) (194.127.2.74)


Dear Bug-Team,

in the function rgb() the argument names is only applied, when alpha is not
missing.
This is due to the substr() applied at the end, which deletes the names of
result.

I guess that preserving the names before substr() and setting them afterwards
again would rectify the problem.

Best regards,
Stefan