[gnome-autoar] Fix segmentation fault when the input archive is empty

[Ting-Wei Lan <lantw src gnome org>]

commit 0300e4b31253779541a6f078ca45bd7a3bd6e7db
Author: Ting-Wei Lan <lantw src gnome org>
Date:   Tue Oct 14 16:46:45 2014 +0800

    Fix segmentation fault when the input archive is empty

 gnome-autoar/autoar-extract.c |   10 ++++++++++
 1 files changed, 10 insertions(+), 0 deletions(-)
---
diff --git a/gnome-autoar/autoar-extract.c b/gnome-autoar/autoar-extract.c
index 65a49d0..c5886e6 100644
--- a/gnome-autoar/autoar-extract.c
+++ b/gnome-autoar/autoar-extract.c
@@ -96,6 +96,7 @@ G_DEFINE_QUARK (autoar-extract, autoar_extract)
 
 #define BUFFER_SIZE (64 * 1024)
 #define NOT_AN_ARCHIVE_ERRNO 2013
+#define EMPTY_ARCHIVE_ERRNO 2014
 
 typedef struct _GFileAndInfo GFileAndInfo;
 
@@ -1797,6 +1798,15 @@ autoar_extract_step_scan_toplevel (AutoarExtract *arextract)
     archive_read_data_skip (a);
   }
 
+  if (pathname_prefix == NULL) {
+    if (priv->error == NULL) {
+      priv->error = g_error_new (AUTOAR_EXTRACT_ERROR, EMPTY_ARCHIVE_ERRNO,
+                                 "\'%s\': %s", priv->source, "empty archive");
+    }
+    archive_read_free (a);
+    return;
+  }
+
   if (r != ARCHIVE_EOF) {
     if (priv->error == NULL) {
       priv->error = autoar_common_g_error_new_a (a, priv->source);