[evolution] Prefer user's value of WEBKIT_DISABLE_COMPOSITING_MODE

[Milan Crha <mcrha src gnome org>]

commit 1d4c91f6e3af63221cb3ed6d64c4660c4cfff54f
Author: Milan Crha <mcrha redhat com>
Date:   Thu Dec 1 11:22:08 2016 +0100

    Prefer user's value of WEBKIT_DISABLE_COMPOSITING_MODE
    
    That way only if the environment variable is not set is populated
    with preferred value by the Evolution, thus users can try whether
    certain WebKitGTK+ version behaves better without a need to recompile
    the evolution.

 src/shell/main.c |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)
---
diff --git a/src/shell/main.c b/src/shell/main.c
index bf0a63b..17fd8a9 100644
--- a/src/shell/main.c
+++ b/src/shell/main.c
@@ -593,8 +593,10 @@ main (gint argc,
        if (!quit) {
                /* Until there will be a proper WebKitGTK+ API for disabling the
                 * accelerated compositing mode, we need to use the environment
-                * variable. See https://bugzilla.gnome.org/show_bug.cgi?id=774067 */
-               g_setenv("WEBKIT_DISABLE_COMPOSITING_MODE", "1", TRUE);
+                * variable. See https://bugzilla.gnome.org/show_bug.cgi?id=774067
+                * Also do not overwrite the variable in case the user has
+                * it already set, thus he/she can override the Evolution's default. */
+               g_setenv ("WEBKIT_DISABLE_COMPOSITING_MODE", "1", FALSE);
 
                /* FIXME WK2 - Look if we still need this it looks like it's not. */
                /* Workaround https://bugzilla.gnome.org/show_bug.cgi?id=683548 */