Close db in stack-blower test

Cherry-picked from Level/leveldown#668

Author: vweevers

test/stack-blower.js

@@ -21,7 +21,12 @@ if (process.argv[2] === 'run') {
     try {
       recurse()
     } catch (e) {
-      process.send('Catchable error at depth ' + depth)
+      // Closing before process exit is normally not needed. This is a
+      // temporary workaround for Level/leveldown#667.
+      db.close(function (err) {
+        if (err) throw err
+        process.send('Catchable error at depth ' + depth)
+      })
     }
   })
 }