broken db: fix assertion in leveldb::InternalKey::Encode, mark base as corrupt

[proller]

Program received signal SIGABRT, Aborted.
__libc_do_syscall () at ../ports/sysdeps/unix/sysv/linux/arm/libc-do-syscall.S:44
44      ../ports/sysdeps/unix/sysv/linux/arm/libc-do-syscall.S: No such file or directory.
#0  __libc_do_syscall () at ../ports/sysdeps/unix/sysv/linux/arm/libc-do-syscall.S:44
#1  0xb6e11ebe in __GI_raise (sig=sig@entry=6) at ../nptl/sysdeps/unix/sysv/linux/raise.c:56
#2  0xb6e14716 in __GI_abort () at abort.c:89
#3  0xb6e0d104 in __assert_fail_base (fmt=0x1 <error: Cannot access memory at address 0x1>, assertion=0x63210 "!rep_.empty()", assertion@entry=0x0,
    file=0x63220 "./db/dbformat.h", file@entry=0xb6ff9000 "", line=171, line@entry=3068948644,
    function=function@entry=0x634b8 <leveldb::InternalKey::Encode() const::__PRETTY_FUNCTION__> "leveldb::Slice leveldb::InternalKey::Encode() const") at assert.c:92
#4  0xb6e0d19a in __GI___assert_fail (assertion=0x0, file=0xb6ff9000 "", line=3068948644,
    function=0x634b8 <leveldb::InternalKey::Encode() const::__PRETTY_FUNCTION__> "leveldb::Slice leveldb::InternalKey::Encode() const") at assert.c:101
#5  0x00049962 in leveldb::InternalKey::Encode (this=0x857fc) at ./db/dbformat.h:171
#6  0x0004ecaa in leveldb::VersionSet::Builder::Apply (this=0xbefff13c, edit=0xbefff0d8) at db/version_set.cc:667
#7  0x0004c436 in leveldb::VersionSet::Recover (this=0x79d20, save_manifest=0xbefff317) at db/version_set.cc:963
#8  0x0003983a in leveldb::DBImpl::Recover (this=0x78350, edit=0xbefff330, save_manifest=0xbefff317) at db/db_impl.cc:303
#9  0x0003d7ae in leveldb::DB::Open (options=..., dbname="map.db", dbptr=0xbefff3a4) at db/db_impl.cc:1498

[googlebot]

Thanks for your pull request. It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

📝 Please visit https://cla.developers.google.com/ to sign.

Once you've signed, please reply here (e.g. I signed it!) and we'll verify. Thanks.

---

• If you've already signed a CLA, it's possible we don't have your GitHub username or you're using a different email address. Check your existing CLA data and verify that your email is set on your git commits.
• If you signed the CLA as a corporation, please let us know the company's name.

[proller]

I signed it!

[googlebot]

CLAs look good, thanks!

[cmumford]

@googlebot rescan