Avoid nullptr dereference on bad rcmap value entry #42034

Job	Run time
build (stm32f7, chibios, 10)	1s
build (stm32h7, chibios, 10)	1s
build (fmuv2-plane, chibios, 10)	2m 25s
build (periph-build, chibios, 10)	1m 16s
build (iofirmware, chibios, 10)	1m 57s
build (CubeOrange-bootloader, chibios, 10)	2m 58s
build (fmuv3-bootloader, chibios, 10)	2m 20s
build (revo-bootloader, chibios, 10)	1s
build (stm32h7-debug, chibios, 10)	1s
build (fmuv3, chibios, 10)	2m 1s
build (revo-mini, chibios, 10)	1s
build (MatekF405-Wing, chibios, 10)	1m 23s
build (CubeOrange-ODID, chibios, 10)	1m 23s
build (CubeRedPrimary-bootloader, chibios, 10)	2m 57s
build (configure-all, chibios, 10)	4m 28s
build (build-options-defaults-test, chibios, 10)	4m 32s
build (signing, chibios, 10)	1s
build (CubeOrange-PPP, chibios, 10)	1m 23s
build (CubeOrange-EKF2, chibios, 10)	1m 26s
build (SOHW, chibios, 10)	1s
build (Pixhawk6X-PPPGW, chibios, 10)	28s
build (new-check, chibios, 10)	58s
	32m 2s

Provide feedback