RFR: 8282948: JDK-8274980 missed correct handling of MACOSX_BUNDLE_BUILD_VERSION

[Magnus Ihse Bursie]

If VERSION_BUILD is empty, we must still store a "0" in MACOSX_BUNDLE_BUILD_VERSION.

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

Commit messages:
 - 8282948: JDK-8274980 missed correct handling of MACOSX_BUNDLE_BUILD_VERSION

Changes: https://git.openjdk.java.net/jdk/pull/7773/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7773&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8282948
  Stats: 6 lines in 1 file changed: 5 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7773.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7773/head:pull/7773

PR: https://git.openjdk.java.net/jdk/pull/7773