ecore-wayland: Doublecheck input validity

Summary:
Most of the other ecore-wayland API will return NULL in the (hopefully
theoretical) case of bad inputs; this API routine should so similarly
for consistency.

Reviewers: zmike, cedric

Subscribers: cedric

Differential Revision: https://phab.enlightenment.org/D2181

src/lib/ecore_wayland/Ecore_Wayland.h

@@ -787,6 +787,8 @@ EAPI Eina_Bool ecore_wl_dnd_drag_get(Ecore_Wl_Input *input, const char *type);
 EAPI void ecore_wl_dnd_drag_types_set(Ecore_Wl_Input *input, const char **types_offered);
 
 /**
+ * @return the data types being offered for drag-and-drop, or NULL on error
+ *
  * @ingroup Ecore_Wl_Dnd_Group
  * @since 1.8
  */

src/lib/ecore_wayland/ecore_wl_dnd.c

@@ -398,6 +398,7 @@ ecore_wl_dnd_drag_types_get(Ecore_Wl_Input *input)
 
    /* check for valid input. if not, get the default one */
    if (!input) input = _ecore_wl_disp->input;
+   if (!input) return NULL;
 
    return &input->data_types;
 }