gengrid: fixed _elm_gengrid_item_edge_check for ELM_FOCUS_DOWN and ELM_FOCUS_UP for...

gengrid: fixed _elm_gengrid_item_edge_check for ELM_FOCUS_DOWN and ELM_FOCUS_UP for normal and horizontal mode

Summary:
Added fixes for:
1.Normal mode: ELM_FOCUS_DOWN and ELM_FOCUS_UP
2.Horizontal mode: ELM_FOCUS_DOWN and ELM_FOCUS_UP

(i)

1|2|3
4|5|6
7|8|9

_elm_gengrid_item_edge_check for ELM_FOCUS_DOWN returns EINA_TRUE for item no.6.
It should not. Fixed this.

(ii)

1|2|3
4|5|6
7

_elm_gengrid_item_edge_check returns EINA_FALSE for ELM_FOCUS_DOWN
for item no. 5 and 6 but EINA_TRUE for item no. 7.
It should return EINA_TRUE for item no. 5 and 6 instead.
Fixed this.

(iii)

1|2|3
4|

_elm_gengrid_item_edge_check returned EINA_FALSE for ELM_FOCUS_UP
for item no. 3. Fixed this.

(iv)

1|4|7
2|5|
3|6|

Horizontal Mode: _elm_gengrid_item_edge_check returned EINA_FALSE
for ELM_FOCUS_DOWN for item no. 7. Fixed this.

(v)

1|4|7
2|5|
3|6|

Horizontal Mode: _elm_gengrid_item_edge_check returned EINA_FALSE
for ELM_FOCUS_UP for item no. 1. Fixed this.

Test Plan: elementary_test -to gengrid2

Reviewers: seoz, raster

CC: singh.amitesh, raster
Differential Revision: https://phab.enlightenment.org/D841

Conflicts:
	src/lib/elm_gengrid.c