Bail after failed compose in nightly-modular.sh

When nightly-modular.sh was added, it wasn't set to check the
exit code from pungi-koji, as nightly.sh does. This was I guess
because it didn't do much after the compose finished at that
time, and the author thought it was OK for the few things it
*did* do to happen on both successful and failed composes.

However, it now does more stuff after compose completion, like
nightly.sh, including trying to generate changelog files and
send out a compose report email. But because the pungi-koji
exit code check is missing, it tries to do these things even
for failed composes. Changelog generation will fail when the
compose failed, and the email that gets sent out will have a
missing compose ID (because NEWCOMPOSE_ID and SHORTCOMPOSE_ID
can't be set properly and will be blank), and will be empty
because the changelog file that's supposed to be read in as the
content of the email isn't there. This is why we are getting
an empty mail with subject "Fedora Modular bikeshed compose
report:  changes" every time a compose fails.

So, let's put that check in just like nightly.sh does.

Signed-off-by: Adam Williamson <awilliam@redhat.com>

nightly-modular.sh

@@ -52,6 +52,9 @@ else
 fi
 
 time $CMD "$@"
+if [ "$?" != "0" ]; then
+    exit 1
+fi
 
 NEWCOMPOSE_ID=$(cat $TARGET_DIR/latest-Fedora-Modular-Bikeshed/COMPOSE_ID)
 SHORTCOMPOSE_ID=$(echo $NEWCOMPOSE_ID|sed -e 's|Fedora-Modular.*-||g')