The UTF-8 regex can occasionally fail on very low memory machines. Reduce the amount of memory it uses.

Merges [32375] to the 4.0 branch.

props pento.
See #32204.

Built from https://develop.svn.wordpress.org/branches/4.0@32397


git-svn-id: http://core.svn.wordpress.org/branches/4.0@32367 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/wp-db.php

@@ -2625,7 +2625,7 @@ class wpdb {
 					';
 				}
 
-				$regex .= '){1,50}                          # ...one or more times
+				$regex .= '){1,40}                          # ...one or more times
 					)
 					| .                                  # anything else
 					/x';