fix encodingmask of DiagnosticInfo

In 2008, before the OpcUa specification was released, the EncodingMask was changed to include the Locale after the LocalizedText. This commit applies the changes necessary to display DiagnosticInfo correctly.

Change-Id: Iad35ff0557eac62a259a63505ebce3e637095136
Reviewed-on: https://code.wireshark.org/review/3259
Reviewed-by: Alexis La Goutte <alexis.lagoutte@gmail.com>
Reviewed-by: Michael Mann <mmann78@netscape.net>