fix(db_sqlite): per_second_deltas survives schema mismatch

When a plugin's cumulative-counter cache table schema does not
match what the current plugin version expects, the internal
insert() call hits an OperationalError. With the default
delete_db_on_operational_error=True it then runs rm_db(conn) -
which closes the connection - and the explicit drop_table(conn) +
recreate path right below blew up with

    sqlite3.ProgrammingError: Cannot operate on a closed database

Hit on production by mysql-aria. Fix: per_second_deltas calls
insert() with delete_db_on_operational_error=False so the
connection stays alive across the schema-mismatch error, and the
plugin-level drop+recreate path can do its work as intended.

Author: markuslf

CHANGELOG.md

@@ -24,6 +24,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixed
 
+* db_sqlite.py: `per_second_deltas()` no longer crashes with `sqlite3.ProgrammingError: Cannot operate on a closed database` when the cache table schema mismatches an earlier plugin version. The internal `insert()` call now uses `delete_db_on_operational_error=False` so the connection survives the schema-mismatch error; the explicit drop/recreate path below operates on a live connection as intended
 * base.py: `oao()` now properly HTML-escapes `&`, `<` and `>` into `&amp;`, `&lt;` and `&gt;` instead of replacing `<` and `>` with apostrophes. The previous implementation destroyed legitimate threshold descriptions like `<= 10` and shell snippets like `echo 1 > /proc/sys/...`, turning them into `'= 10` and `echo 1 ' /proc/sys/...` in plugin output. HTML-based web UIs (Icinga Web, Naemon-Adagios) render the entities back to the original characters; terminal viewers see the literal entities, which preserves the information. The XSS-protection goal of the original change is still met
 * url.py: `fetch()` with HTTP digest authentication and `insecure=True` now actually disables certificate verification. Previously the digest auth path silently lost the SSL context
 * url.py: `fetch()` with `no_proxy=True` now applies the `timeout` parameter. Previously the no-proxy path called `opener.open(request)` without a timeout, so hangs were only caught by the outer plugin wrapper

db_sqlite.py

@@ -28,7 +28,7 @@
 """
 
 __author__ = 'Linuxfabrik GmbH, Zurich/Switzerland'
-__version__ = '2026051101'
+__version__ = '2026051102'
 
 import csv
 import hashlib
@@ -921,7 +921,11 @@ def per_second_deltas(filename, name, counters):
 
     row = {'name': name, 'timestamp': time.now()}
     row.update(counters)
-    ok, _ = insert(conn, row)
+    # Pass `delete_db_on_operational_error=False` so a schema mismatch leaves
+    # the connection open. We then drop+recreate the table ourselves below;
+    # the default `True` would `rm_db(conn)` (close + delete) and break the
+    # subsequent drop_table() with "Cannot operate on a closed database".
+    ok, _ = insert(conn, row, delete_db_on_operational_error=False)
     if not ok:
         # Schema mismatch from a previous plugin version (different counter
         # columns or NOT NULL constraints). Rebuild the table from the
@@ -933,7 +937,7 @@ def per_second_deltas(filename, name, counters):
             close(conn)
             return None
         create_index(conn, 'name')
-        ok, _ = insert(conn, row)
+        ok, _ = insert(conn, row, delete_db_on_operational_error=False)
         if not ok:
             close(conn)
             return None