RFR: 8253948: Memory leak in ImageFileReader [v3]

[Zhengyu Gu]

> ImageFileReader allocates ImageModuleData in ImageFileReader::open(), but never free.
> 
> Also renamed module_data to _module_data to be consistent with other member variables.
> 
> Test:
> - [x] tier1 on Linux x86_64

Zhengyu Gu has updated the pull request incrementally with one additional commit since the last revision:

  More indentation fixes

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/490/files
  - new: https://git.openjdk.java.net/jdk/pull/490/files/18326c81..c066d4ec

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=490&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=490&range=01-02

  Stats: 4 lines in 1 file changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk/pull/490.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/490/head:pull/490

PR: https://git.openjdk.java.net/jdk/pull/490