message: Fix possible dereferencing of invalid iterator
  if low was equal to m_labelAddrOffsetMap.end(), the code
  would dereference an invalid iterator. Flip the conditions
  to ensure that the validity check is performed first.
diff: @@ -260,7 +260,7 @@ long ProgramViewer::addressForBlock(QTextBlock block) const {
  auto low = m_labelAddrOffsetMap.lower_bound(lineNumber);
  - if (lineNumber < low->first && (low == m_labelAddrOffsetMap.begin())) {
  + if ((low == m_labelAddrOffsetMap.begin()) && lineNumber < low->first) {
  // The line number is less that the position of the first offset block; address is directly inferred from
  // linenumber.
  return calcAddressFunc(adjustedLineNumber);
  