evas: Fix can't open tiff file on loader

Summary:
Evas can't open tiff file because of no implement in client read api.
I wrote codes simply for open.

Test Plan: self

Reviewers: jpeg, cedric, jypark

Subscribers: stefan_schmidt

Differential Revision: https://phab.enlightenment.org/D4857

src/modules/evas/image_loaders/tiff/evas_image_load_tiff.c

@@ -42,11 +42,15 @@ struct TIFFRGBAMap {
 };
 
 static tsize_t
-_evas_tiff_RWProc(thandle_t handle EINA_UNUSED,
-                  tdata_t data EINA_UNUSED,
-                  tsize_t size EINA_UNUSED)
+_evas_tiff_RWProc(thandle_t handle,
+                  tdata_t data,
+                  tsize_t size)
 {
-   return 0;
+   TIFFRGBAMap *map = (TIFFRGBAMap*) handle;
+   if (!data) return 0;
+   memcpy(data, map->mem, size);
+
+   return size;
 }
 
 static toff_t