[Rpm-maint] [rpm-software-management/rpm] btree_next hangs when encountering deleted entries (Issue #4132)

[Yoav Alon]

yoav-orca created an issue (rpm-software-management/rpm#4132)

**Describe the bug**
running rpm query on a bdb backend with deleted entry results in an infinite loop.
```
rpm --define "_db_backend bdb_ro" --nosignature --dbpath /tmp/rpmdb -q abc
```

**To Reproduce**
Steps to reproduce the behavior:
1. Download attached database file [minimal-rpmdb-bdbro-hang-repro.tar.gz](https://github.com/user-attachments/files/25749721/minimal-rpmdb-bdbro-hang-repro.tar.gz)
2. timeout 10s rpm --define "_db_backend bdb_ro" --nosignature --dbpath /tmp/rpmdb -q abc
3. echo $? (will be 124)

Please link or attach the packages or spec files involved.

**Expected behavior**
The command should not hang

**Output**
If applicable, add copy of the output on the command line or a screenshots to help explain your problem.

**Environment**
 - OS / Distribution: 
```
PRETTY_NAME="Debian GNU/Linux 13 (trixie)"
NAME="Debian GNU/Linux"
VERSION_ID="13"
VERSION="13 (trixie)"
VERSION_CODENAME=trixie
DEBIAN_VERSION_FULL=13.3
ID=debian
HOME_URL="https://www.debian.org/"
SUPPORT_URL="https://www.debian.org/support"
BUG_REPORT_URL="https://bugs.debian.org/"
```
 - Version: `RPM version 4.20.1`

**Additional context**
I have tracked the issue to:
```diff
diff --git a/lib/backend/bdb_ro.c b/lib/backend/bdb_ro.c
@@ -461,8 +461,11 @@ static int btree_next(struct bdb_cur *cur)
 	voff = *(uint16_t *)(cur->page + 28 + 2 * cur->idx);
 	if (koff + 3 > pagesize || voff + 3 > pagesize)
 	    return -1;
-	if ((cur->page[koff + 2] & 0x80) != 0 || (cur->page[voff + 2] & 0x80) != 0)
-	    continue;	/* ignore deleted */
+	if ((cur->page[koff + 2] & 0x80) != 0 || (cur->page[voff + 2] & 0x80) != 0) {
+	    cur->idx += 2;	/* deleted key/value pair, advance to next entry */
+	    continue;
+	}
 	if (btree_getkv(cur, &cur->key, &cur->keyov, koff))
 	    return -1;
```




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