imgtool: fix "align" script error #1814

Job	Run time
config (RELEASE 2,4,6 SIGNATURE)	8m 56s
config (RELEASE 2,4,6 SIGNATURE LOW)	13m 28s
config (RELEASE 2,4,6 SIGNATURE MEDIUM)	17m 24s
config (RELEASE 8,10 SIGNATURE)	6m 37s
config (RELEASE 8,10 SIGNATURE LOW)	9m 9s
config (RELEASE 8,10 SIGNATURE MEDIUM)	11m 52s
config (MINSIZEREL 2,4,6 SIGNATURE)	14m 49s
config (MINSIZEREL 2,4,6 SIGNATURE LOW)	19m 51s
config (MINSIZEREL 2,4,6 SIGNATURE MEDIUM)	23m 49s
config (MINSIZEREL 8,10 SIGNATURE)	10m 21s
config (MINSIZEREL 8,10 SIGNATURE LOW)	13m 41s
config (MINSIZEREL 8,10 SIGNATURE MEDIUM)	16m 17s
	2h 46m 14s

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