lib-sieve: util: realpath: Fixed assertion in path_normalize().

The invariant was using the wrong variable for comparison, causing it to trigger
erraticly.

src/lib-sieve/util/realpath.c

@@ -96,7 +96,7 @@ static int path_normalize(const char *path, bool resolve_links,
 			}
 
 			/* copy segment to normalized path */
-			i_assert(p + seglen < npath + asize);
+			i_assert((npath_pos + seglen) < (npath + asize));
 			(void)memmove(npath_pos, p, seglen);
 			npath_pos += seglen;
 		}