Avoid infinite loop in ftoa_engine #51609

Job	Run time
build (stm32h7, chibios, 10)	3m 18s
build (CubeOrange-bootloader, chibios, 10)	59s
build (iofirmware, chibios, 10)	1m 57s
build (stm32h7-debug, chibios, 10)	2m 35s
build (fmuv2-plane, chibios, 10)	1m 43s
build (fmuv3-bootloader, chibios, 10)	1m 0s
build (periph-build, chibios, 10)	3m 36s
build (stm32f7, chibios, 10)	3m 35s
build (fmuv3, chibios, 10)	5m 45s
build (revo-bootloader, chibios, 10)	49s
build (MatekF405-Wing, chibios, 10)	4m 41s
build (revo-mini, chibios, 10)	4m 17s
build (CubeOrange-ODID, chibios, 10)	2m 34s
build (configure-all, chibios, 10)	13m 33s
build (CubeOrange-EKF2, chibios, 10)	1m 52s
build (Pixhawk6X-PPPGW, chibios, 10)	1m 31s
build (signing, chibios, 10)	2m 37s
build (CubeRedPrimary-bootloader, chibios, 10)	52s
build (CubeOrange-PPP, chibios, 10)	2m 0s
build (SOHW, chibios, 10)	3m 33s
build (new-check, chibios, 10)	4m 35s
build (build-options-defaults-test, chibios, 10)	6m 56s
	1h 14m 18s

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