Make mmm stop if it can't find an Android.mk in a directory you give it.
diff --git a/envsetup.sh b/envsetup.sh
index ad8e2ff..a06ff8c 100644
--- a/envsetup.sh
+++ b/envsetup.sh
@@ -666,6 +666,7 @@
                     ARGS="$ARGS showcommands"
                 else
                     echo "No Android.mk in $DIR."
+                    return 1
                 fi
             fi
         done