Don't try to update empty process history ID

[wmtan]

This is a fix for a bug that has been in place since CMSSW_6_2_0.
The problem was hit by Erik Butz when he tried to read a file written with CMSSW_3_2_5.
For files written in CMSSW_5_0_0 and later, actual FED raw data is recorded as having been created in a process called "LHC" with a module label of "rawDataCollector". If a file written prior to CMSSW_5_0_0 is read in CMSSW_5_0_0 or later, this "LHC" process is added retroactively, which affects the process history. The process history must then be retroactively modified.
This worked fine until CMSSW_6_2_0, when a bug was introduced. There is a map used to map the old process history to the new. In 6_2_0, the entry for an empty old process history was incorrectly omitted from the map. Real raw data prior to CMSSW_5_0_0 had an empty process history. So, the process history ID for real raw data was not found in the map. and a fatal assert fired.
The fix is to simply add the missing entry to the map.

[cmsbuild]

A new Pull Request was created by @wmtan for CMSSW_6_2_X_SLHC.

Don't try to update empty process history ID

It involves the following packages:

IOPool/Input

@cmsbuild, @Degano, @Dr15Jones, @ktf, @nclopezo can you please review it and eventually sign? Thanks.
You can sign-off by replying to this message having '+1' in the first line of your reply.
You can reject by replying to this message having '-1' in the first line of your reply.
@andersonjacob, @mark-grimes you are the release manager for this.
You can merge this pull request by typing 'merge' in the first line of your comment.

[wmtan]

Please don't sign this yet. This fix has a problem. The request will be updated shortly. Closing temporarily.

[cmsbuild]

Pull request #2521 was updated. @cmsbuild, @Degano, @Dr15Jones, @ktf, @nclopezo can you please check and sign again.

[wmtan]

The fix has been corrected.