ubi-utils: FIX DIVISION BY ZERO in ubinize.c

ubi-utils: FIX DIVISION BY ZERO in ubinize.c

Report of the static analyzer:
Variable vi->alignment, whose possible value set allows a zero value at ubinize.c:375, is used as a denominator at ubinize.c:410.

If you look at the code more closely, it will be clear that the vi->alignment parameter is obtained from an external file passed as a command line argument.

A check was also performed if you pass a test.ini file of the following type to the input:

[jffs2-volume]
mode=ubi
image=../jffs2.img
vol_id=1
vol_size=30MiB
vol_type=dynamic
vol_name=jffs2_volume
vol_flags=autoresize
vol_alignment=0

and execute the command:

./ubinize -o ubi.img -p 16KiB -m 512 -s 256 test.ini

we will get the result:

Floating point exception (core dumped)

Corrections explained:
Updated the validation logic for vi->alignment:
- Replaced the check for negative alignment (`vi->id < 0`) with a more comprehensive check for non-positive alignment (`vi->alignment <= 0`).
- Updated the corresponding error message to reflect the requirement for a positive volume alignment.
This ensures more robust validation and improves error clarity when invalid alignment values are encountered.

Triggers found by static analyzer Svace.

Signed-off-by: Anton Moryakov <ant.v.moryakov@gmail.com>
Reviewed-by: Zhihao Cheng <chengzhihao1@huawei.com>
Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>