[jdk13u-dev] RFR: 8222079: Don't use memset to initialize fields decode_env constructor in disassembler.cpp

[Yuri Nesterenko]

I'd like to port it to 13u, too. Applies totally clean.

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Commit messages:
 - Backport 9c2e15364c76f1189ed269c453b9ecbd559275b5

Changes: https://git.openjdk.java.net/jdk13u-dev/pull/86/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk13u-dev&pr=86&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8222079
  Stats: 78 lines in 1 file changed: 42 ins; 2 del; 34 mod
  Patch: https://git.openjdk.java.net/jdk13u-dev/pull/86.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk13u-dev pull/86/head:pull/86

PR: https://git.openjdk.java.net/jdk13u-dev/pull/86