Remove dead code from openssl_spki_new() implementation (#18752)

If s is not NULL, the length can't be <= 0 because we at least append
`spkac` in the string, which is non-empty.
I noticed this condition because if it were actually possible to
execute, then it would leak memory.

ext/openssl/openssl.c

@@ -652,10 +652,6 @@ cleanup:
 	if (spki != NULL) {
 		NETSCAPE_SPKI_free(spki);
 	}
-
-	if (s && ZSTR_LEN(s) <= 0) {
-		RETVAL_FALSE;
-	}
 }
 /* }}} */