(sparse_add_map): Fixed improper initializations

of sparse_map_size. We assume that whatever number it contains
describes adequately the current size of sparse_map. The only
number we need to reset is sparse_map_avail.

src/sparse.c

@@ -189,7 +189,7 @@ sparse_scan_file (struct tar_sparse_file *file)
     return false;
   clear_block (buffer);
 
-  file->stat_info->sparse_map_size = 0;
+  file->stat_info->sparse_map_avail = 0;
   file->stat_info->archive_file_size = 0;
 
   if (!tar_sparse_scan (file, scan_begin, NULL))
@@ -626,7 +626,7 @@ oldgnu_get_sparse_info (struct tar_sparse_file *file)
   int ext_p;
   static enum oldgnu_add_status rc;
 
-  file->stat_info->sparse_map_size = 0;
+  file->stat_info->sparse_map_avail = 0;
   for (i = 0; i < SPARSES_IN_OLDGNU_HEADER; i++)
     {
       rc = oldgnu_add_sparse (file, &h->oldgnu_header.sp[i]);
@@ -752,7 +752,7 @@ star_get_sparse_info (struct tar_sparse_file *file)
   int ext_p;
   static enum oldgnu_add_status rc;
 
-  file->stat_info->sparse_map_size = 0;
+  file->stat_info->sparse_map_avail = 0;
 
   if (h->star_in_header.prefix[0] == '\0'
       && h->star_in_header.sp[0].offset[10] != '\0')