RFR: 8373626: [asan] read past end of buffer in sun.awt.image.ImagingLib.convolveBI

[Phil Race]

Some of the medialib native functions implementing Convolve read data from arrays when it is not needed or used instead of reading just what is needed and used.
This is detected as a read out of bounds. It is limited and hasn't been seen to result in any crashes without ASAN, and the OOB values that are read are never used so there's a very limited problem.
The changes here make the mlib_ImageConv_*nw.c files match what happens in the mlib_ImageConv_*ext.c files which read just the data they need.
The changes are fairly mechanical but there could be copy/paste errors for a reviewer to find.

Not easy to provide a test case, building with --enable-asan is needed and for me it works only on macOS.
I did that and ran all our existing automated tests on our CI systems.

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Commit messages:
 - 8373626

Changes: https://git.openjdk.org/jdk/pull/29257/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29257&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8373626
  Stats: 435 lines in 7 files changed: 357 ins; 54 del; 24 mod
  Patch: https://git.openjdk.org/jdk/pull/29257.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29257/head:pull/29257

PR: https://git.openjdk.org/jdk/pull/29257