evas_engine: remove logically dead code

Summary:
"plane" exception value is already filtered at line 1791.
execution cannot reach this statement.

Reviewers: cedric, Jaehyun_Cho

Reviewed By: Jaehyun_Cho

Differential Revision: https://phab.enlightenment.org/D5973

src/modules/evas/engines/software_generic/evas_engine.c

@@ -1899,7 +1899,6 @@ eng_image_data_slice_add(void *engdata, void *image,
              for (int y = 0; y < (h / 2); y++)
                cs_data[h + (h / 2) + y] = slice->bytes + (y * stride);
           }
-        else goto fail;
         evas_common_image_colorspace_dirty(im);
         break;