The patch for the "release blocker" is easy. The following lines must be moved
near the end of the repair function, the check must be performed whenever
repairing, not only if you are below the highest repair skill level:
-8<---------
if (it->max_durability < 1) {
  it->max_durability = 1;
}
-8<---------

On the other hand, the quality issues cannot be repaired through patches WITHOUT
reclassifying anything, because there is no consistent definition of "bad" and
"good" in comparison to "normal" in the current code.

There is a solution without influence on the current game mechanics: we don't
alter the calculations, so the non-uniform value distribution remains as is, but
"reclassify" items at the end of the creation and repair functions and set the
quality state there. If an item "intended to become good/bad" in the first place
isn't actually exceptionally good or bad after rolling the dice, it would be
consistently reclassified according to the actual outcome of the process.

This needs a new definition in non-overlapping maximum dirability percentage
ranges, however, which I wanted to discuss here before submitting patches
according to my personal taste which would then be postponed because they
contain a mix of bug fixes and my own game balance preferences.