RFR: 8303930: Fix ConstantUtils.skipOverFieldSignature void case return value

[liach]

This typo doesn't allow creation of malformed ClassDesc or MethodTypeDesc, but it produces an erroneous exception on certain inputs. Running `java.lang.constant.MethodTypeDesc.ofDescriptor("(IIIII[[[V)I")` in Jshell 19.0.2 throws StringIndexOutOfBoundsException, and throws IllegalArgumentException in the Jshell for this patch.

-------------

Commit messages:
 - 8303930: Fix ConstantUtils.skipOverFieldSignature void case return value

Changes: https://git.openjdk.org/jdk/pull/12964/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12964&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8303930
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/12964.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12964/head:pull/12964

PR: https://git.openjdk.org/jdk/pull/12964