Fix SeedExtensionTrajectoryFilter when it is disabled

[makortel]

It turns out that in some corner cases the SeedExtensionTrajectoryFilter, with its default configuration parameters, stops trajectory propagation, in contrast to the intent of the default values (that would be "no effect"). These cases are essentially such that the trajectory has at most as many measurements as the seed, and no lost hits (i.e. the condition of looseTBC), and occur e.g. in muonSeededStepInOut (where seeds have many hits) when rebuilding the trajectory in the seed region (can lead to lost hits).

Here are MultiTrackValidator plots from 1000 TTbar+PU events (red is with this PR) https://mkortela.web.cern.ch/mkortela/tracking/validation/CMSSW_8_1_X_seedExtension/
The effect becomes more noticeable if we start to reject trajectories stopped by SeedExtension (as in #14356).

Tested in CMSSW_8_1_X_2016-05-09-2300, expecting tiny changes in tracking.

@rovere @VinInn: I decided to use the value of seedExtension parameter directly to dictate whether the filter should be enabled or not (<= 0 for disabled, > 0 for enabled) instead of introducing a new flag, since these interpretations of the parameter values are compatible with the current intended uses.

[cmsbuild]

A new Pull Request was created by @makortel (Matti Kortelainen) for CMSSW_8_1_X.

It involves the following packages:

TrackingTools/TrajectoryFiltering

@cmsbuild, @cvuosalo, @slava77, @davidlange6 can you please review it and eventually sign? Thanks.
@GiacomoSguazzoni, @rovere, @VinInn, @bellan, @gpetruc, @dgulhan this is something you requested to watch as well.
@slava77, @Degano, @smuzaffar you are the release manager for this.

cms-bot commands are list here #13028

[slava77]

@cmsbuild please test

[cmsbuild]

The tests are being triggered in jenkins.
https://cmssdt.cern.ch/jenkins/job/ib-any-integration/12944/console

[cmsbuild]

+1
Tested at: 2e2d878
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-14472/12944/summary.html

[cmsbuild]

Comparison is ready
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-14472/12944/summary.html

[slava77]

+1

for #14472 2e2d878

• code change is as described
• jenkins tests pass and show a number of small differences starting from track reconstruction or related plots
• local tests with higher statistics show up to o(0.1%) effect on the number of tracks and a slightly higher fraction in changes of the track parameters and in objects downstream from tracking, no adverse effects apparently. Plots in https://mkortela.web.cern.ch/mkortela/tracking/validation/CMSSW_8_1_X_seedExtension/ show small to negligible effect on tracking with higher statistics.

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_8_1_X IBs (tests are also fine). This pull request requires discussion in the ORP meeting before it's merged. @slava77, @davidlange6, @Degano, @smuzaffar

[slava77]

@davidlange6
please merge at your earliest. This is needed to proceed with #14356
Thanks.

[davidlange6]

+1