fix: check that frozen.build exists before trying to access it

[conorh]

If there is a compilation where frozen.build is not generated for some reason then the check here would fail and throw an exception:

   Could not freeze FILE_NAME: Cannot read property 'hash' of undefined

Added check to see if the build exists, and then fall through to regenerate if it does not.

[larixer]

@mzgoddard Can we have this merged?

[larixer]

@mzgoddard Could you please, please review this PR and merge it? This problem is really a showstopper for us.

[eddieferrer]

Any update on merging this in?

[bovas85]

bump

[elevatebart]

Can anyone look at the travis tests, see why they are not passing?

[ansballard]

So the tests aren't passing because npm run lint returns errors (calls prettier --list-different ...). Running npm run lint:fix should get travis to pass, as confirmed on a branch I made from this one. I actually went back a year or so in the travis build history and not a single run has succeeded, so we could merge this as is, especially since it's been tested via use of hard-source-webpack-plugin-fixed-hashbug.

TL;DR this looks perfectly safe to merge, with or without fixing the liner errors that are already in master anyway.

[dazjean]

m