Fix warnings and listener return values

Description

The overall goal of this MR is to address compiler warnings. Almost all of the changes should result in identical behavior. However, there are a small set of modifications which actually do correct an identified defect.

There were several listeners structured in the following manner:

if (expression) {
    statement
    true
}
false

The objective was clearly to return true when the condition was handled; however, true ended up being unused, and it returned false regardless. The code was modified to use an else block, as shown below:

if (expression) {
    statement
    true
} else false

Motivation and Context

Resolves approximately 330 warnings.

How Has This Been Tested?

Some modifications were not fully tested as the changes should not result in different runtime behavior.

Types of changes

• Bug fix (non-breaking change which fixes an issue)

Checklist

• I have read the CONTRIBUTING section of the README document.