Fixed compiler warnings

[COM8]

In preparation for the build system rewrite where -Wall -Wextra -Wpedantic -Werror will be set by default, this PR fixes all warnings reported.

I removed

if (this->mQueueIndex < 0) {
    throw std::runtime_error("Kompute Sequence queue index not provided");
}

without any replacement since mQueueIndex will be always set in the constructor anyway.

Fixes: #278

[axsaucedo]

Nice - this is really good thank you @COM8 , we can now close #278