DNS key verification: Fix handling keys without an e-mail address

If an PGP key is stored in an RPM database without a "packager" RPM
header, or without an e-mail address there, DNS verification crashed
on converting the undefined address into a DNS domain. That was the
case of Fedora 13 key:

    # dnf-3 upgrade
    Traceback (most recent call last):
      File "/usr/bin/dnf-3", line 62, in <module>
        main.user_main(sys.argv[1:], exit_code=True)
      File "/usr/lib/python3.12/site-packages/dnf/cli/main.py", line 201, in user_main
        errcode = main(args)
                  ^^^^^^^^^^
      File "/usr/lib/python3.12/site-packages/dnf/cli/main.py", line 67, in main
        return _main(base, args, cli_class, option_parser_class)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      File "/usr/lib/python3.12/site-packages/dnf/cli/main.py", line 106, in _main
        return cli_run(cli, base)
               ^^^^^^^^^^^^^^^^^^
      File "/usr/lib/python3.12/site-packages/dnf/cli/main.py", line 122, in cli_run
        cli.run()
      File "/usr/lib/python3.12/site-packages/dnf/cli/cli.py", line 1040, in run
        self._process_demands()
      File "/usr/lib/python3.12/site-packages/dnf/cli/cli.py", line 741, in _process_demands
        self.base.fill_sack(
      File "/usr/lib/python3.12/site-packages/dnf/base.py", line 403, in fill_sack
        dnf.dnssec.RpmImportedKeys.check_imported_keys_validity()
      File "/usr/lib/python3.12/site-packages/dnf/dnssec.py", line 286, in check_imported_keys_validity
        keys = RpmImportedKeys._query_db_for_gpg_keys()
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      File "/usr/lib/python3.12/site-packages/dnf/dnssec.py", line 276, in _query_db_for_gpg_keys
        email = re.search('<(.*@.*)>', packager).group(1)
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      File "/usr/lib64/python3.12/re/__init__.py", line 177, in search
        return _compile(pattern, flags).search(string)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    TypeError: expected string or bytes-like object, got 'NoneType'

This patch defends the crash at two places: In
_query_db_for_gpg_keys() because here we know a NEVRA of the key
and can produce a meaningful message. And in _cache_miss() because
we can get there independenly and called email2location() would also
crash.

dnf/dnssec.py

@@ -185,6 +185,10 @@ def _cache_miss(input_key):
         if ctx.add_ta_file("/var/lib/unbound/root.key") != 0:
             logger.debug("Unbound context: Failed to add trust anchor file")
 
+        if input_key.email == None:
+            logger.debug("A key has no associated e-mail address")
+            return Validity.ERROR
+
         status, result = ctx.resolve(email2location(input_key.email),
                                      RR_TYPE_OPENPGPKEY, unbound.RR_CLASS_IN)
         if status != 0:
@@ -273,7 +277,13 @@ def _query_db_for_gpg_keys():
         return_list = []
         for pkg in packages:
             packager = dnf.rpm.getheader(pkg, 'packager')
-            email = re.search('<(.*@.*)>', packager).group(1)
+            if packager == None:
+                email = None
+            else:
+                email = re.search('<(.*@.*)>', packager).group(1)
+            if email == None:
+                logger.debug(any_msg(_("Exempting key package {} from a validation because it's not bound to any e-mail address").format(dnf.rpm.getheader(pkg, 'nevra'))))
+                continue
             description = dnf.rpm.getheader(pkg, 'description')
             # Extract Radix-64-encoded PGP key. Without armor headers and
             # a checksum.