loader.js: Try to carry on even if some scripts fail to load
loader.js: Try to carry on even if some scripts fail to load

For eg. some BUILD_FILES are optional - the order doesn't really matter, so we ought to keep loading
whatever we can (i.e. if we don't have Capstone, we should still be able to load
libwabt).

Note: Even without this change, v86 would have kept trying to load and run, ignoring any 404s; this
change just makes it likelier that we'll ignore ignorable errors.

copy/v86,copy/v86,copy/v86,copy/v86,copy/v86,copy/v86,copy/v86