RFR: 8280842: Access violation in ciTypeFlow::profiled_count

[Roland Westrelin]

When the test() method is osr compiled, the exception handler is
marked as a loop head. It has 2 backedges at the 2 throw statements in
the method. ciTypeFlow expects to find some profile data at the
backedges but hotspot doesn't collect counters for athrow. The fix is
to turn the assert into an actual check.

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Commit messages:
 - fix & test

Changes: https://git.openjdk.java.net/jdk/pull/7298/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7298&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8280842
  Stats: 62 lines in 2 files changed: 60 ins; 1 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7298.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7298/head:pull/7298

PR: https://git.openjdk.java.net/jdk/pull/7298