[gcab] extract: learn to rewind if needed

[Marc-Andre Lureau <malureau src gnome org>]

commit 616e77a54964aee8754acefbea4e76a15529dfa7
Author: Marc-André Lureau <marcandre lureau gmail com>
Date:   Wed Mar 9 18:05:06 2016 +0100

    extract: learn to rewind if needed
    
    In some cases, files my point to previously treated offset. Let's rewind
    in this case.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=763377

 libgcab/gcab-folder.c |   10 ++++++++++
 1 files changed, 10 insertions(+), 0 deletions(-)
---
diff --git a/libgcab/gcab-folder.c b/libgcab/gcab-folder.c
index da14044..e724097 100644
--- a/libgcab/gcab-folder.c
+++ b/libgcab/gcab-folder.c
@@ -404,6 +404,16 @@ gcab_folder_extract (GCabFolder *self,
 
         u4 usize = file->cfile.usize;
         u4 uoffset = file->cfile.uoffset;
+
+        /* let's rewind if need be */
+        if (uoffset < nubytes) {
+            if (!g_seekable_seek (G_SEEKABLE (data), self->cfolder.offsetdata,
+                                  G_SEEK_SET, cancellable, error))
+                goto end;
+            bzero(&cdata, sizeof(cdata));
+            nubytes = 0;
+        }
+
         while (usize > 0) {
             if ((nubytes + cdata.nubytes) <= uoffset) {
                 nubytes += cdata.nubytes;