[gdk-pixbuf] tests: Fix signed/unsigned handling in pixdata_equal()

[Philip Withnall <pwithnall src gnome org>]

commit ebb88fe9661b0f493267d4bfaddec1023d8f6641
Author: Philip Withnall <withnall endlessm com>
Date:   Tue Jan 17 08:43:43 2017 +0000

    tests: Fix signed/unsigned handling in pixdata_equal()
    
    The return values from the GdkPixbuf getters are signed, so assign them
    to signed variables and then check that the returned values are
    non-negative.
    
    Coverity IDs: 1388535, 1388536, 1388537
    
    https://bugzilla.gnome.org/show_bug.cgi?id=777374

 tests/test-common.c |    6 +++++-
 1 files changed, 5 insertions(+), 1 deletions(-)
---
diff --git a/tests/test-common.c b/tests/test-common.c
index a75655f..2f4f3a4 100644
--- a/tests/test-common.c
+++ b/tests/test-common.c
@@ -194,7 +194,7 @@ pixdata_equal (GdkPixbuf  *test,
   if (memcmp (gdk_pixbuf_get_pixels (test), gdk_pixbuf_get_pixels (ref),
           gdk_pixbuf_get_byte_length (test)) != 0)
     {
-      guint x, y, width, height, n_channels, rowstride;
+      gint x, y, width, height, n_channels, rowstride;
       const guchar *test_pixels, *ref_pixels;
 
       rowstride = gdk_pixbuf_get_rowstride (test);
@@ -204,6 +204,10 @@ pixdata_equal (GdkPixbuf  *test,
       test_pixels = gdk_pixbuf_get_pixels (test);
       ref_pixels = gdk_pixbuf_get_pixels (ref);
 
+      g_assert_cmpint (width, >=, 0);
+      g_assert_cmpint (height, >=, 0);
+      g_assert_cmpint (n_channels, >=, 0);
+
       for (y = 0; y < height; y++)
         {
           for (x = 0; x < width; x++)