Exit early from generateModuleBuildActions on error

generateModuleBuildActions was continuing to call GenerateBuildActions
on all modules even after one returned an error.  This could cause a
later module to panic because it was missing information that was
supposed to be generated by the module that returned an error, hiding
the earlier error message.

If a module returns an error, stop triggering any new goroutines to
call GenerateBuildActions on later modules.