RFR: 8278185: Custom JRE cannot find non-ASCII named module inside

[Toshio Nakamura]

Could you review this fix?

Problem:
Custom JRE generated by jlink cannot find non-ASCII named modules included inside the JRE.

Cause and fix:
If module or package name was composed by ASCII then non-ASCII characters, 
ImageStringsReader:stringFromByteBufferMatches() miscalculated the length of matched string. The first part of ASCII characters was missing. This patch corrected the value.

Testing:
tier1 and tier2 on Linux have no regression.
I wasn't able to create an automate test for this issue. I appreciate any advice.

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Commit messages:
 - 8278185: Custom JRE cannot find non-ASCII named module inside

Changes: https://git.openjdk.java.net/jdk/pull/6693/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6693&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8278185
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6693.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6693/head:pull/6693

PR: https://git.openjdk.java.net/jdk/pull/6693