Fix issue 13682: false negative: nullPointerRedundantCheck (multiple conditions, regression)

[pfultz2]

No description provided.

[firewave]

Very nice.

The following ones are lacking the details but I do not think this needs to be fixed in the context of this PR and adding TODO tests and a ticket about this might be sufficient.

lib/checkstl.cpp:552:25: style: Condition 'containerToken' is always true [knownConditionTrueFalse]
                    if (containerToken && containerToken->variable() && containerToken->variable()->isReference()) {
                        ^

lib/checkcondition.cpp:458:70: style: Condition '!cond2->astOperand2()' is always false [knownConditionTrueFalse]
        if (!Token::Match(cond2, "&|==") || !cond2->astOperand1() || !cond2->astOperand2())
                                                                     ^

[pfultz2]

@chrchr-github @danmar Can you review?