[geary] Fix build on s390x/ppc64.

[Michael Gratton <mjog src gnome org>]

commit ee76477366f98454a3102c7c015dd27a33ff2680
Author: Michael James Gratton <mike vee net>
Date:   Mon Sep 25 12:04:28 2017 +1000

    Fix build on s390x/ppc64.
    
    Patch courtesy of Gianfranco Costamagna.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=783882

 src/client/web-process/web-process-extension.vala |   12 +++++++++---
 1 files changed, 9 insertions(+), 3 deletions(-)
---
diff --git a/src/client/web-process/web-process-extension.vala 
b/src/client/web-process/web-process-extension.vala
index fba5384..ee89139 100644
--- a/src/client/web-process/web-process-extension.vala
+++ b/src/client/web-process/web-process-extension.vala
@@ -86,7 +86,9 @@ public class GearyWebExtension : Object {
     private bool should_load_remote_images(WebKit.WebPage page) {
         bool should_load = false;
         WebKit.Frame frame = page.get_main_frame();
-        JS.GlobalContext context = frame.get_javascript_global_context();
+        // Explicit cast fixes build on s390x/ppc64. Bug 783882
+        JS.GlobalContext context = (JS.GlobalContext)
+            frame.get_javascript_global_context();
         try {
             JS.Value ret = execute_script(
                 context, "geary.allowRemoteImages", int.parse("__LINE__")
@@ -103,7 +105,9 @@ public class GearyWebExtension : Object {
 
     private void remote_image_load_blocked(WebKit.WebPage page) {
         WebKit.Frame frame = page.get_main_frame();
-        JS.GlobalContext context = frame.get_javascript_global_context();
+        // Explicit cast fixes build on s390x/ppc64. Bug 783882
+        JS.GlobalContext context = (JS.GlobalContext)
+            frame.get_javascript_global_context();
         try {
             execute_script(
                 context, "geary.remoteImageLoadBlocked();", int.parse("__LINE__")
@@ -118,7 +122,9 @@ public class GearyWebExtension : Object {
 
     private void selection_changed(WebKit.WebPage page) {
         WebKit.Frame frame = page.get_main_frame();
-        JS.GlobalContext context = frame.get_javascript_global_context();
+        // Explicit cast fixes build on s390x/ppc64. Bug 783882
+        JS.GlobalContext context = (JS.GlobalContext)
+            frame.get_javascript_global_context();
         try {
             execute_script(
                 context, "geary.selectionChanged();", int.parse("__LINE__")