[solang] Correctly detect failure in extracting thumbnails using Exiv2

[Debarshi Ray <debarshir src gnome org>]

commit 020bfa8735e0e83a4da9fb13581b8b3ef8f92db8
Author: Debarshi Ray <rishi gnu org>
Date:   Sat Dec 5 20:27:14 2009 +0200

    Correctly detect failure in extracting thumbnails using Exiv2
    
    + Since Exiv2::ExifThumbC::writeFile returns the number of bytes
      written a return value of zero is also an error.
    + Do not overwrite thumbnail_generated with true even when the
      generation has failed.
    
    Fixes: https://savannah.nongnu.org/bugs/?27538

 src/attribute/thumbnail.cpp |    8 +++++---
 1 files changed, 5 insertions(+), 3 deletions(-)
---
diff --git a/src/attribute/thumbnail.cpp b/src/attribute/thumbnail.cpp
index c88f362..2835ff1 100644
--- a/src/attribute/thumbnail.cpp
+++ b/src/attribute/thumbnail.cpp
@@ -166,12 +166,14 @@ Thumbnail::generate(Exiv2::ExifData & exifData,
     {
         // Extract from exif if present.
         Exiv2::ExifThumb thumbnail( exifData );
-        if (-1 == thumbnail.writeFile(get_path().c_str()))
+        if (0 <= thumbnail.writeFile(get_path().c_str()))
         {
             thumbnail_generated = false;
         }
-
-        thumbnail_generated = true;
+        else
+        {
+            thumbnail_generated = true;
+        }
 
         //Update resoulution info
         Thumbnail::Resolution res;