Minor refactor: move 2 lines

src/fellow_cache.c

@@ -2022,9 +2022,6 @@ fellow_busy_body_seg_alloc(struct fellow_busy *fbo,
 	AZ(fds->seg.off);
 	AZ(fds->seg.size);
 
-	want = fellow_rndup(fc->ffd,  want);
-	AZ(want & FELLOW_BLOCK_ALIGN);
-
 	fdr = fbr->reg;
 	if (fdr == NULL || fbr->len == fdr->size) {
 
@@ -2047,6 +2044,8 @@ fellow_busy_body_seg_alloc(struct fellow_busy *fbo,
 	spc = fdr->size - fbr->len;
 	AZ(spc & FELLOW_BLOCK_ALIGN);
 
+	want = fellow_rndup(fc->ffd,  want);
+	AZ(want & FELLOW_BLOCK_ALIGN);
 	if (spc < want)
 		want = spc;