Fix size class calculation for sec

Due to a bug in sec initialization, the number of cached size classes
was equal to 198. The bug caused the creation of more than a hundred of
unused bins, although it didn't affect the caching logic.

test/unit/sec.c

@@ -46,6 +46,7 @@ test_sec_init(sec_t *sec, pai_t *fallback, size_t nshards, size_t max_alloc,
 
 	bool err = sec_init(TSDN_NULL, sec, base, fallback, &opts);
 	assert_false(err, "Unexpected initialization failure");
+	assert_u_ge(sec->npsizes, 0, "Zero size classes allowed for caching");
 }
 
 static inline edata_t *