[easytag] Add for loop condition to File_Tag check

[David King <davidk src gnome org>]

commit 23ce98865177a48bc1578af878a718c07e4e2449
Author: David King <amigadave amigadave com>
Date:   Tue Jun 30 17:52:26 2015 +0100

    Add for loop condition to File_Tag check
    
    Avoid a crash when checking the difference between two files without
    images.

 src/file_tag.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)
---
diff --git a/src/file_tag.c b/src/file_tag.c
index b0cf164..cab85eb 100644
--- a/src/file_tag.c
+++ b/src/file_tag.c
@@ -453,7 +453,8 @@ et_file_tag_detect_difference (const File_Tag *FileTag1,
     }
 
     /* Picture */
-    for (pic1 = FileTag1->picture, pic2 = FileTag2->picture; ;
+    for (pic1 = FileTag1->picture, pic2 = FileTag2->picture;
+         pic1 || pic2;
          pic1 = pic1->next, pic2 = pic2->next)
     {
         if (et_picture_detect_difference (pic1, pic2))