WPDB: When removing invalid characters from utf8 strings in older versions of PHP, the regex was too large to be compiled.

See #21212


git-svn-id: https://develop.svn.wordpress.org/trunk@30366 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/wp-db.php

@@ -2411,7 +2411,7 @@ class wpdb {
 						|   [\xE1-\xEC][\x80-\xBF]{2}
 						|   \xED[\x80-\x9F][\x80-\xBF]
 						|   [\xEE-\xEF][\x80-\xBF]{2}
-						){1,100}                         # ...one or more times
+						){1,50}                          # ...one or more times
 					)
 					| .                                  # anything else
 					/x';