RFR: 8267424: CTW: C1 fails with "State must not be null"

[Igor Veresov]

Range check elimination may need a block at the root of the compilation to insert its predicates. Make sure we have one.

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Commit messages:
 - Ensure there is a header block with RCE

Changes: https://git.openjdk.java.net/jdk/pull/4437/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4437&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8267424
  Stats: 4 lines in 1 file changed: 2 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4437.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4437/head:pull/4437

PR: https://git.openjdk.java.net/jdk/pull/4437