[evince] Fix overflow checks in tiff backend

[Jason Crain <jcrain src gnome org>]

commit e02fe9170ad0ac2fd46c75329c4f1d4502d4a362
Author: Jason Crain <jcrain src gnome org>
Date:   Sat Dec 2 20:24:33 2017 -0600

    Fix overflow checks in tiff backend
    
    The overflow checks in tiff_document_render and
    tiff_document_get_thumbnail don't work when optimizations are enabled.
    Change the checks so they don't rely on undefined behavior.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=788980

 backend/tiff/tiff-document.c |   12 ++++++------
 1 files changed, 6 insertions(+), 6 deletions(-)
---
diff --git a/backend/tiff/tiff-document.c b/backend/tiff/tiff-document.c
index 8f40934..7bf95c2 100644
--- a/backend/tiff/tiff-document.c
+++ b/backend/tiff/tiff-document.c
@@ -284,12 +284,12 @@ tiff_document_render (EvDocument      *document,
                return NULL;                
        }
        
-       bytes = height * rowstride;
-       if (bytes / rowstride != height) {
+       if (height >= INT_MAX / rowstride) {
                g_warning("Overflow while rendering document.");
                /* overflow */
                return NULL;
        }
+       bytes = height * rowstride;
        
        pixels = g_try_malloc (bytes);
        if (!pixels) {
@@ -374,15 +374,15 @@ tiff_document_get_thumbnail (EvDocument      *document,
        if (width <= 0 || height <= 0)
                return NULL;                
 
-       rowstride = width * 4;
-       if (rowstride / 4 != width)
+       if (width >= INT_MAX / 4)
                /* overflow */
                return NULL;                
+       rowstride = width * 4;
         
-       bytes = height * rowstride;
-       if (bytes / rowstride != height)
+       if (height >= INT_MAX / rowstride)
                /* overflow */
                return NULL;                
+       bytes = height * rowstride;
        
        pixels = g_try_malloc (bytes);
        if (!pixels)