Fix a segfault that can occur if a malloc fails in ATTACH in shared-cache mode.

FossilOrigin-Name: e37137376a2b23062e2625b5285299b33630b326
diff --git a/test/attachmalloc.test b/test/attachmalloc.test
index 30841ce..cc506be 100644
--- a/test/attachmalloc.test
+++ b/test/attachmalloc.test
@@ -60,4 +60,17 @@
   ATTACH 'test2.db' AS db1;
 }
 
+set enable_shared_cache [sqlite3_enable_shared_cache 1]
+sqlite3 dbaux test2.db
+dbaux eval {SELECT * FROM sqlite_master}
+do_malloc_test attachmalloc-3 -sqlbody {
+  SELECT * FROM sqlite_master;
+  ATTACH 'test2.db' AS two;
+} -cleanup {
+  db eval { DETACH two }
+}
+dbaux close
+sqlite3_enable_shared_cache $enable_shared_cache
+
+
 finish_test