dashboard/app: fix merging of renamed bugs
dashboard/app: fix merging of renamed bugs

We need to search old bugs by all alternative titles
rather than only the current main title.
If a bug is renamed its old title becomes one of alternatives titles.
It's hard to test because this code is invoked only
during migration from old schema.

Update #1575

google/syzkaller,google/syzkaller,google/syzkaller,xairy/syzkaller,xairy/syzkaller,xairy/syzkaller,google/syzkaller,xairy/syzkaller,xairy/syzkaller,google/syzkaller,google/syzkaller,xairy/syzkaller,xairy/syzkaller,google/syzkaller