Ah, indeed, I somehow missed that. Though, there is no good reason for it being unsigned either; as the actual type in SSL API's is of type int. Another argument of type int is cast to unsigned just for the comparison on line 4419, and unsigned int counters i and j are used in function _setup_ssl_threads.
The variable could be safely changed to `size_t` (along with those index variables) without it affecting anything at all, as it is a static variable within that module and only used to hold a size of an array, and never passed back to another function.