RFR: 8334164: The fix for JDK-8322811 should use _filename.is_set() rather than strcmp()

[Sonia Zaldana Calles]

Hi all, 

This PR addresses [8334164](https://bugs.openjdk.org/browse/JDK-8334164). 

Testing: 
- [x] Verified specifying the literal `vm_memory_map_<pid>.txt` as the map name does not replace `<pid>`. 
- [x] Verified `<pid>` is still appropriately replaced if a file path is not specified. 

Thanks, 
Sonia

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Commit messages:
 - 8334164: The fix for JDK-8322811 should use _filename.is_set() rather than strcmp()

Changes: https://git.openjdk.org/jdk/pull/19706/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19706&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8334164
  Stats: 5 lines in 1 file changed: 2 ins; 2 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/19706.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19706/head:pull/19706

PR: https://git.openjdk.org/jdk/pull/19706