RFR: 8296957: One more cast in SAFE_SIZE_NEW_ARRAY2

[Sergey Bylokhov]

Implementation of SAFE_SIZE_NEW_ARRAY2 in the `sizecalc.h` missed one cast to the size_t

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Commit messages:
 - 8296957: One more cast in SAFE_SIZE_NEW_ARRAY2

Changes: https://git.openjdk.org/jdk/pull/11253/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11253&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8296957
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/11253.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11253/head:pull/11253

PR: https://git.openjdk.org/jdk/pull/11253