web: fix PHP warning in login action. #3718

Job	Run time
client-armv6-build	2m 46s
libs-build	6m 50s
client-arm-build	4m 4s
apps-build	9m 46s
libs-cmake-build	7m 7s
client-arm64-build	3m 18s
client-x86-build	3m 12s
client-x86_64-build	4m 1s
manager-build (assembleRelease)	3m 56s
manager-build (assembleXiaomi_release)	4m 48s
manager-build (assembleArmv6_release)	4m 42s
manager-build (jacocoTestReportDebug)	6m 49s
	1h 1m 19s

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