ecore_evas: add double header include safety

Reported-By: https://lgtm.com/projects/g/Enlightenment/efl
Reviewed-by: Chris Michael <cp.michael@samsung.com>
Differential Revision: https://phab.enlightenment.org/D10887

src/modules/ecore_evas/engines/extn/ecore_evas_extn_engine.h

@@ -1,3 +1,6 @@
+#ifndef _ECORE_EVAS_EXTN_ENGINE_H_
+#define _ECORE_EVAS_EXTN_ENGINE_H_
+
 #ifdef HAVE_CONFIG_H
 # include <config.h>
 #endif
@@ -222,3 +225,5 @@ struct _Ipc_Data_Ev_Key_Down
    unsigned int timestamp;
    Evas_Event_Flags event_flags;
 };
+
+#endif /*_ECORE_EVAS_EXTN_ENGINE_H_*/