[epiphany] PDF: Fix back navigation skipping one page

[Michael Catanzaro <mcatanzaro src gnome org>]

commit 920bcd841e00e008cdec746028243cc15aa45dc7
Author: Jan-Michael Brummer <jan brummer tabos org>
Date:   Fri Jan 18 17:45:41 2019 +0100

    PDF: Fix back navigation skipping one page

 src/window-commands.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)
---
diff --git a/src/window-commands.c b/src/window-commands.c
index 2c0d74df4..9e53f69e2 100644
--- a/src/window-commands.c
+++ b/src/window-commands.c
@@ -668,8 +668,12 @@ window_cmd_navigation (GSimpleAction *action,
   web_view = EPHY_GET_WEBKIT_WEB_VIEW_FROM_EMBED (embed);
 
   if (strstr (g_action_get_name (G_ACTION (action)), "back")) {
-    ephy_embed_set_mode (embed, EPHY_EMBED_MODE_WEB_VIEW);
-    webkit_web_view_go_back (web_view);
+    gboolean in_document_mode = ephy_embed_get_mode (embed) == EPHY_EMBED_MODE_EVINCE_DOCUMENT;
+
+    if (in_document_mode)
+      ephy_embed_set_mode (embed, EPHY_EMBED_MODE_WEB_VIEW);
+    else
+      webkit_web_view_go_back (web_view);
 
     gtk_widget_grab_focus (GTK_WIDGET (embed));
   } else {