[gthumb] image viewer: do not try do paint surfaces with invalid size

[Paolo Bacchilega <paobac src gnome org>]

commit ea9415a703097f805ba227fedda908dfe72c4e90
Author: Paolo Bacchilega <paobac src gnome org>
Date:   Mon Dec 16 20:44:47 2019 +0100

    image viewer: do not try do paint surfaces with invalid size

 gthumb/gth-image-viewer.c | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)
---
diff --git a/gthumb/gth-image-viewer.c b/gthumb/gth-image-viewer.c
index ca7160f6..58d346ae 100644
--- a/gthumb/gth-image-viewer.c
+++ b/gthumb/gth-image-viewer.c
@@ -2613,6 +2613,7 @@ gth_image_viewer_paint (GthImageViewer  *self,
                        cairo_filter_t   filter)
 {
        int    original_width;
+       int    surface_width;
        double zoom_level;
        double src_dx;
        double src_dy;
@@ -2621,13 +2622,12 @@ gth_image_viewer_paint (GthImageViewer  *self,
        double dwidth;
        double dheight;
 
-       cairo_save (cr);
-
-       cairo_rectangle (cr, 0, 0, self->visible_area.width, self->visible_area.height);
-       cairo_clip (cr);
+       surface_width = cairo_image_surface_get_width (surface);
+       if (surface_width <= 0)
+               return;
 
        gth_image_viewer_get_original_size (self, &original_width, NULL);
-       zoom_level = self->priv->zoom_level * ((double) original_width / cairo_image_surface_get_width 
(surface));
+       zoom_level = self->priv->zoom_level * ((double) original_width / surface_width);
        src_dx = (double) src_x / zoom_level;
        src_dy = (double) src_y / zoom_level;
        dest_dx = (double) dest_x / zoom_level;
@@ -2635,6 +2635,13 @@ gth_image_viewer_paint (GthImageViewer  *self,
        dwidth = (double) width / zoom_level;
        dheight = (double) height / zoom_level;
 
+       if ((dwidth < 1) || (dheight < 1))
+               return;
+
+       cairo_save (cr);
+
+       cairo_rectangle (cr, 0, 0, self->visible_area.width, self->visible_area.height);
+       cairo_clip (cr);
        cairo_scale (cr, zoom_level, zoom_level);
        cairo_set_source_surface (cr, surface, dest_dx - src_dx, dest_dy - src_dy);
        cairo_pattern_set_filter (cairo_get_source (cr), filter);