RFR: 1785: Do not always add CSR_UPDATE_MARKER when CSR bot finds withdrawn CSR Issue

[Zhao Song]

In [SKARA-1728](https://bugs.openjdk.org/browse/SKARA-1728), I said that 'if we find a withdrawn pr, we need to add CSR_UPDATE_MARKER to the pr body.', yes, we need to add CSR_UPDATE_MARKER, but there is a prerequisite which is that our status message **doesn't** contain this withdrawn issue. Without the prerequisite, the CSR bot will always add CSR_UPDATE_MARKER when it finds a withdrawn CSR Issue and the pr body will be updated very frequently(looks like the bot go berserk). 

This issue is same as [SKARA-1673](https://bugs.openjdk.org/browse/SKARA-1673). I discovered this issue and fixed it, but I am silly enough to make the same mistake again.

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Commit messages:
 - SKARA-1785
 - SKARA-1785

Changes: https://git.openjdk.org/skara/pull/1455/files
 Webrev: https://webrevs.openjdk.org/?repo=skara&pr=1455&range=00
  Issue: https://bugs.openjdk.org/browse/SKARA-1785
  Stats: 9 lines in 1 file changed: 8 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/skara/pull/1455.diff
  Fetch: git fetch https://git.openjdk.org/skara pull/1455/head:pull/1455

PR: https://git.openjdk.org/skara/pull/1455