openconnect: fix off-by-one while condition #27007

Job	Run time
Test Formalities / Test Formalities	17s
Add formality check labels	4s
Feeds Package Test Build / Test arm_cortex-a9_vfpv3-d16	15m 29s
Feeds Package Test Build / Test mips_24kc	15m 50s
Feeds Package Test Build / Test i386_pentium-mmx	17m 15s
Feeds Package Test Build / Test mipsel_24kc	16m 52s
Feeds Package Test Build / Test aarch64_generic	16m 31s
Feeds Package Test Build / Test arm_cortex-a15_neon-vfpv4	17m 29s
Feeds Package Test Build / Test riscv64_generic	17m 16s
Feeds Package Test Build / Test powerpc_8548	16m 34s
Feeds Package Test Build / Test x86_64	17m 23s
Feeds Package Test Build / Test powerpc_464fp	17m 1s
	2h 48m 1s

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