tree-wide: check if return value of lseek() and friends is negative

We usually check return value of syscalls or glibc functions by it is
negative or not, something like that `if (stat(path, &st) < 0)`.
Let's also use the same style for lseek() and friends even the type of
their return value is off_t.

Note, fseeko() returns int, instead of off_t.

src/basic/io-util.c

@@ -283,7 +283,7 @@ ssize_t sparse_write(int fd, const void *p, size_t sz, size_t run_length) {
                                         return -EIO;
                         }
 
-                        if (lseek(fd, n, SEEK_CUR) == (off_t) -1)
+                        if (lseek(fd, n, SEEK_CUR) < 0)
                                 return -errno;
 
                         q += n;