RFR: 8265607: Avoid decrementing when no Symbol was created in ~SignatureStream

[Claes Redestad]

This patch trivially avoids decrementing refcount on java/lang/Object (a permanent symbol) that is used as a sentinel when the SignatureStream found no Symbols during parse. This is the common case, especially during early VM startup

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Commit messages:
 - missing semi
 - Skip refcount decrement if no Symbols were created during signature parse

Changes: https://git.openjdk.java.net/jdk/pull/3596/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3596&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8265607
  Stats: 6 lines in 1 file changed: 6 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3596.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3596/head:pull/3596

PR: https://git.openjdk.java.net/jdk/pull/3596