`case` where `in` is on a new line don't get highlighted correctly

[alexr00]

The code with a problem is:

case "$1"\
  in
esac

It looks like:

It should look like:

Originally from @cD1rtX3 in https://github.com/microsoft/vscode/issues/276874

[cD1rtX3]

Duplicate of #115, but thank you!