The field is marked as "the offset in the file (in clusters)", but it
was being used like this
`cluster_size*(nums)+mapping->info.file.offset`, which is incorrect.

Additionally, removed the `abort` when `first_mapping_index` does not
match, as this matches the case when adding new clusters for files, and
its inevitable that we reach this condition when doing that if the
clusters are not after one another, so there is no reason to `abort`
here, execution continues and the new clusters are written to disk
correctly.

Signed-off-by: Amjad Alsharafi <amjadsharafi10@gmail.com>
---
 block/vvfat.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/block/vvfat.c b/block/vvfat.c
index ab342f0743..cb3ab81e29 100644
--- a/block/vvfat.c
+++ b/block/vvfat.c
@@ -1408,7 +1408,7 @@ read_cluster_directory:
 
         assert(s->current_fd);
 
-        offset=s->cluster_size*(cluster_num-s->current_mapping->begin)+s->current_mapping->info.file.offset;
+        offset=s->cluster_size*((cluster_num - s->current_mapping->begin) + s->current_mapping->info.file.offset);
         if(lseek(s->current_fd, offset, SEEK_SET)!=offset)
             return -3;
         s->cluster=s->cluster_buffer;
@@ -1929,8 +1929,8 @@ get_cluster_count_for_direntry(BDRVVVFATState* s, direntry_t* direntry, const ch
                         (mapping->mode & MODE_DIRECTORY) == 0) {
 
                     /* was modified in qcow */
-                    if (offset != mapping->info.file.offset + s->cluster_size
-                            * (cluster_num - mapping->begin)) {
+                    if (offset != s->cluster_size
+                            * ((cluster_num - mapping->begin) + mapping->info.file.offset)) {
                         /* offset of this cluster in file chain has changed */
                         abort();
                         copy_it = 1;
@@ -1944,7 +1944,6 @@ get_cluster_count_for_direntry(BDRVVVFATState* s, direntry_t* direntry, const ch
 
                     if (mapping->first_mapping_index != first_mapping_index
                             && mapping->info.file.offset > 0) {
-                        abort();
                         copy_it = 1;
                     }
 
@@ -2404,7 +2403,7 @@ static int commit_mappings(BDRVVVFATState* s,
                         (mapping->end - mapping->begin);
             } else
                 next_mapping->info.file.offset = mapping->info.file.offset +
-                        mapping->end - mapping->begin;
+                        (mapping->end - mapping->begin);
 
             mapping = next_mapping;
         }
-- 
2.45.0