RFR: 8296912: C2: CreateExNode::Identity fails with assert(i < _max) failed: oob: i=1, _max=1

[Tobias Hartmann]

The fix for [JDK-8284358](https://bugs.openjdk.org/browse/JDK-8284358) added code that aggressively removes dead subgraphs when detecting an unreachable Region by walking up the CFG and replacing all nodes by top (because they must be unreachable as well). In this case, we detect that `280 Region` is unreachable from root and replace `276 Catch` by top while walking up the CFG:

![Screenshot from 2022-11-16 12-53-56](https://user-images.githubusercontent.com/5312595/202174104-9437914a-cb38-401c-b0fd-d6ca849969b0.png)

Code in `CreateExNode::Identity` does not expect `292 CatchProj` to have a top input when processing `305 CreateEx`. The fix is to simply add a `in(0)->in(0)->is_Catch()` check.

Thanks,
Tobias

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Commit messages:
 - 8296912: C2: CreateExNode::Identity fails with assert(i < _max) failed: oob: i=1, _max=1

Changes: https://git.openjdk.org/jdk/pull/11181/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11181&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8296912
  Stats: 30 lines in 2 files changed: 23 ins; 1 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/11181.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11181/head:pull/11181

PR: https://git.openjdk.org/jdk/pull/11181