Add asserts to avoid null pointer dereferences

[wmtan]

Recently, several relvals in the 7_1_X IB's have segfaulted in RootInputFileSequence::readOneSpecified().
That function dereferences a pointer without first checking for a null pointer.
This function adds an assert to that function, and to a few other functions in the same source file, to always check RootInputFileSequence::rootFile_, a pointer, for null before dereferencing it.
The segfaults are not reproducible, but this pull request may help solve the problem by checking for null pointer dereferences.
Some standardization of white space in the same file was also done, and one iterator loop was replaced by a C++11 range for loop.
range for loop.

[cmsbuild]

A new Pull Request was created by @wmtan for CMSSW_7_1_X.

Add asserts to avoid null pointer derefeences

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.
@ktf you are the release manager for this.
You can merge this pull request by typing 'merge' in the first line of your comment.

[Dr15Jones]

+1

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_7_1_X IBs unless changes or unless it breaks tests. @ktf can you please take care of it?

[cmsbuild]

+1
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-2284/16/summary.html

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_7_1_X IBs unless changes (tests are also fine). @ktf can you please take care of it?