[jdk13u-dev] RFR: 8285591: [11] add signum checks in DSA.java engineVerify

[Andrew John Hughes]

This change was part of a security fix, JDK-8277233, for 17u during the April update. The rest of 8277233 did not apply to older releases, as it concerned code added to src/jdk.crypto.ec/share/classes/sun/security/ec/ECDSAOperations.java by JDK-8237218 in 15u.

However, the additional checks in src/java.base/share/classes/sun/security/provider/DSA.java that were included in the patch are applicable to older releases.

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Commit messages:
 - Backport bf3438c5dc993b96d089cabb5318bfc64a6904a3

Changes: https://git.openjdk.java.net/jdk13u-dev/pull/353/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk13u-dev&pr=353&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8285591
  Stats: 3 lines in 1 file changed: 1 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk13u-dev/pull/353.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk13u-dev pull/353/head:pull/353

PR: https://git.openjdk.java.net/jdk13u-dev/pull/353