[jdk17u] RFR: 8272131: PhaseMacroExpand::generate_slow_arraycopy crash when clone null CallProjections.fallthrough_ioproj

[Tobias Hartmann]

Backport of [JDK-8272131](https://bugs.openjdk.java.net/browse/JDK-8272131). Applies cleanly.

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Commit messages:
 - 8272131: PhaseMacroExpand::generate_slow_arraycopy crash when clone null CallProjections.fallthrough_ioproj

Changes: https://git.openjdk.java.net/jdk17u/pull/21/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk17u&pr=21&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8272131
  Stats: 75 lines in 2 files changed: 71 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk17u/pull/21.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk17u pull/21/head:pull/21

PR: https://git.openjdk.java.net/jdk17u/pull/21