openconnect: fix off-by-one while condition #27043

Job	Run time
Test Formalities / Test Formalities	16s
Add formality check labels	5s
Feeds Package Test Build / Test aarch64_generic	31m 50s
Feeds Package Test Build / Test arm_cortex-a15_neon-vfpv4	29m 8s
Feeds Package Test Build / Test arm_cortex-a9_vfpv3-d16	23m 14s
Feeds Package Test Build / Test i386_pentium-mmx	33m 55s
Feeds Package Test Build / Test mips_24kc	29m 32s
Feeds Package Test Build / Test mipsel_24kc	25m 34s
Feeds Package Test Build / Test x86_64	28m 35s
Feeds Package Test Build / Test riscv64_generic	37m 7s
Feeds Package Test Build / Test powerpc_8548	26m 25s
Feeds Package Test Build / Test powerpc_464fp	29m 20s
	4h 55m 1s

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