[NFC] Source maps: Simplify the code and add comments (#5912)

Almost entirely trivial, except for this part:

-  if (nextDebugLocation.availablePos == 0 &&
-      nextDebugLocation.previousPos <= pos) {
+  if (nextDebugLocation.availablePos == 0) {
      return;

I believe removing the extra check has no effect. Removing it does not change
anything in the test suite, and logically, if we set availablePos to 0 then we
definitely want to return here - we set it to 0 to indicate there is nothing left
to read, which is what the code after it does.

As a result, we can remove the previousPos field entirely.

0 files changed, 0 insertions, 0 deletions