Allocate seglists for the worst case object size

Fixes one case for #22

src/fellow_cache.c

@@ -2208,9 +2208,16 @@ fellow_body_seglist_alloc(struct fellow_busy *fbo,
 
 	assert(fbo->sz_estimate > fbo->sz_returned);
 
-	sz = fbo->sz_estimate - fbo->sz_returned;
-	sz >>= chunk_exponent;
-	assert(sz <= UINT16_MAX);
+	if (fbo->grown) {
+		sz = fbo->fc->tune->objsize_max - fbo->sz_dskalloc;
+		sz >>= MIN_FELLOW_BITS;
+		sz++;
+	} else {
+		sz = fbo->sz_estimate - fbo->sz_returned;
+		sz >>= chunk_exponent;
+	}
+	if (sz > UINT16_MAX)
+		sz = UINT16_MAX;
 	ldsegs = (uint16_t)sz;
 	ldsegs++;