gnu: zathura: Fix plugin path regression.

eb6a5dab5c (gnu: zathura: Update to 0.3.9)
silently broke Zathura's (Guix-specific) ZATHURA_PLUGIN_PATH mechanism.

My environment was so filthy that all happened to work just fine, but as
usual Marius was right and the patch needed tweaking.

* gnu/packages/patches/zathura-plugindir-environment-variable.patch:
Tweak.

gnu/packages/patches/zathura-plugindir-environment-variable.patch

@@ -8,15 +8,15 @@ different file formats) called ZATHURA_PLUGIN_PATH. Command line option
 -p still takes precedence.
 
 Patch by Paul van der Walt <paul@denknerd.org>
+Adjusted for Zathura 0.3.9 by Tobias Geerinckx-Rice <me@tobias.gr>
 ---
  zathura/zathura.c | 7 +++++++
  1 file changed, 7 insertions(+)
 
 diff --git a/zathura/zathura.c b/zathura/zathura.c
-index 589dd28..375ec54 100644
 --- a/zathura/zathura.c
 +++ b/zathura/zathura.c
-@@ -413,6 +413,13 @@ zathura_set_plugin_dir(zathura_t* zathura, const char* dir)
+@@ -597,6 +597,13 @@ zathura_set_plugin_dir(zathura_t* zathura, const char* dir)
    g_return_if_fail(zathura != NULL);
    g_return_if_fail(zathura->plugins.manager != NULL);
  
@@ -28,8 +28,5 @@ index 589dd28..375ec54 100644
 +    dir = g_getenv("ZATHURA_PLUGIN_PATH");
 +
    if (dir != NULL) {
-     girara_list_t* paths = girara_split_path_array(dir);
-     GIRARA_LIST_FOREACH(paths, char*, iter, path)
--- 
-2.3.1
-
+     set_plugin_dir(zathura, dir);
+ #ifdef ZATHURA_PLUGINDIR