ZMySQLDA: fix string_literal usage

MySQLdb's string_literal is a method from the C API and the name is not
natural for python programmers, because it manipulates bytes. It
supports str, unless they have non ASCII characters, so it's better to
always pass bytes.

On python2, this change repairs a regression visible when searching
catalog with translated related keys. This regression was introduced in
the merge of zope4 support, more specifically with 610972af (py3:
Update Shared.DC.ZRDB.{sqltest,sqlvar} monkey patches., 2022-04-16),
because with the new version of the patches this method gets passed
unicode strings, which is fine, unless they contain non ASCII characters.

product/ZMySQLDA/DA.py

@@ -89,6 +89,7 @@ $Id: DA.py,v 1.4 2001/08/09 20:16:36 adustman Exp $''' % database_type
 __version__='$Revision: 1.4 $'[11:-2]
 
 import os
+import six
 from collections import defaultdict
 from weakref import WeakKeyDictionary
 import transaction
@@ -172,6 +173,8 @@ class Connection(DABase.Connection):
             # any reason, that would generate an infinite loop.
             self.connect(self.connection_string)
             connection = self._v_database_connection
+        if not isinstance(v, six.binary_type):
+            v = v.encode('utf-8')
         return connection.string_literal(v)
 
 

product/ZMySQLDA/db.py

@@ -466,6 +466,8 @@ class DB(TM):
         return items, result
 
     def string_literal(self, s):
+        # This method accepts bytes or str with only ASCII characters
+        # and return bytes.
         return self.db.string_literal(s)
 
     def _begin(self, *ignored):