Fix wrong overlay manipulation

[igorpecovnik]

Description

Addressing non working overlay management.

Issue reference: Closing #360

Testing Procedure

• Set overlay on Odroid M1

223 bytes read in 5 ms (43 KiB/s)
Applying kernel provided DT overlay rockchip-rk3568-hk-i2c0.dtbo
254 bytes read in 4 ms (61.5 KiB/s)
Applying kernel provided DT overlay rockchip-rk3568-hk-uart1.dtbo

• Set overay on Bpi M2 (h3)

339 bytes read in 3 ms (110.4 KiB/s)
Applying kernel provided DT overlay sun8i-h3-analog-codec.dtbo
502 bytes read in 4 ms (122.1 KiB/s)
Applying kernel provided DT overlay sun8i-h3-uart2.dtbo

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have ensured that my changes do not introduce new warnings or errors
• No new external dependencies are included
• Changes have been tested and verified
• I have included necessary metadata in the code, including associative arrays

[The-going]

84778cc
A little more is needed here.

...
	local overlayconf="/boot/armbianEnv.txt"
	local overlaydir="$(find /boot/dtb/ -name overlay -and -type d)";
	local overlay_prefix=$(awk -F"=" '/overlay_prefix/ {print $1}' $ovrlayconf)
	if ! grep -q $overlay_prefix ${overlaydir}/*.dtbo; then
		echo "Invalid overlay_prefix $overlay_prefix"; exit 1
	fi

	while true; do
		local options=()
...

[The-going]

That's what I was thinking.
After we have set the overlay dir variable, we need to check it. If it is empty, then a message to the user.
The user can install\assemble a broken\someone else's package.
After we have received the value of the overlay prefix from the file that is being edited by the user, we also need to check it.
The overlay_prefix variable cannot be empty.
Otherwise, grep will hang.