drivers: modem: cmd_handler: save 1 char for NUL in match_buf
drivers: modem: cmd_handler: save 1 char for NUL in match_buf

For parsing purposes we need to add a NUL to the end of match_buf.

When there is no CR/LF in the incoming rx bufs then we fill match_buf
to its max size.  This ended up with an off by one error which was
overflowing match_buf into the following data.

To account for this, let's fill the buffer to size - 1 so that we
leave room for the NUL at the end and stop corrupting data.

Signed-off-by: Michael Scott <a17fed27eaa842282862ff7c1b9c8395a26ac320@foundries.io>

finikorg/zephyr,Vudentz/zephyr,nashif/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,finikorg/zephyr,galak/zephyr,galak/zephyr,finikorg/zephyr,galak/zephyr,Vudentz/zephyr,Vudentz/zephyr,finikorg/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,Vudentz/zephyr,finikorg/zephyr,nashif/zephyr,galak/zephyr,Vudentz/zephyr