RFR: 8345374: Ubsan: runtime error: division by zeroavoid divide by zero

[Kim Barrett]

Please review this change to G1HeapSizingPolicy to avoid a float division by
zero when calculating the maximum desired capacity with a MaxHeapFreeRatio
value of 100%.

Testing: mach5 tier1 with G1 and MaxHeapFreeRatio=100.

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Commit messages:
 - avoid divide by zero

Changes: https://git.openjdk.org/jdk/pull/22893/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22893&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8345374
  Stats: 8 lines in 1 file changed: 8 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/22893.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22893/head:pull/22893

PR: https://git.openjdk.org/jdk/pull/22893