fix unlock in addDevice of membership

[jidalong]

What type of PR is this?
/kind bug

What this PR does / why we need it:
a lock was in line 195-197:

if delta {
  context.Lock(device.ID)
}

unlock was in line 251-253:

if delta {
  context.Unlock(device.ID)
}

PR #3348 add log err if convert membership failed , if we use "continue" in line 244 before unlock, it may cause not relase lock as mentioned, so here we should remove it.

Does this PR introduce a user-facing change?:
NONE

[gy95]

LGTM

[jidalong]

LGTM

@gy95 Sorry to disturb, maybe kubeedge project need label '/lgtm' instead of 'LGTM' :)

[gy95]

this is waiting for approve @fisherxu :)

[jidalong]

this is waiting for approve @fisherxu :)

OKey~Thanks

[zc2638]

Hello @jidalong,
Because this project is internationally oriented, and English is the international common language.
It is recommended that all submissions contain only English.
Could you change the title to pure English?
Thanks.

[jidalong]

Hello @jidalong, Because this project is internationally oriented, and English is the international common language. It is recommended that all submissions contain only English. Could you change the title to pure English? Thanks.

@zc2638 Okey，Done.

[zc2638]

/lgtm
/assign @fisherxu

[gy95]

/lgtm

[fisherxu]

/approve

[kubeedge-bot]

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