tar-util: add missing dlopen libarchive

Otherwise, if the library is not loaded yet, these functions will fail.

Note, currently, all callers of tar_x/tar_c() load libarchive before
calling them. So, this should not change any behavior. Just for safety
and following our usual coding style.

src/shared/tar-util.c

@@ -749,6 +749,10 @@ int tar_x(int input_fd, int tree_fd, TarFlags flags) {
         assert(input_fd >= 0);
         assert(tree_fd >= 0);
 
+        r = dlopen_libarchive(LOG_DEBUG);
+        if (r < 0)
+                return r;
+
         _cleanup_(archive_read_freep) struct archive *a = NULL;
         a = sym_archive_read_new();
         if (!a)
@@ -1605,6 +1609,10 @@ int tar_c(int tree_fd, int output_fd, const char *filename, int hardlink_db_fd,
         assert(tree_fd >= 0);
         assert(output_fd >= 0);
 
+        r = dlopen_libarchive(LOG_DEBUG);
+        if (r < 0)
+                return r;
+
         _cleanup_(archive_write_freep) struct archive *a = sym_archive_write_new();
         if (!a)
                 return log_oom();