[OpenJDK 2D-Dev] RFR: 8269223: -Xcheck:jni WARNINGs working with fonts on Linux

[Maxim Kartashev]

Added an `ExceptionCheck()` followed by `ExceptionDescribe()` and `ExceptionClear()` immediately after the Java calls made from the callback function `ReadTTFontFileFunc()` in `freetypeScaler.c`. 

The exception(s) need to be cleared because we're not returning immediately to Java that would've been able to handle them gracefully. And in order not to loose the exception entirely (even though the return value would also indicate an error condition), print out the exception with `ExceptionDescribe()` to aid in debugging.

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Commit messages:
 - 8269223: -Xcheck:jni WARNINGs working with fonts on Linux

Changes: https://git.openjdk.java.net/jdk/pull/4572/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4572&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8269223
  Stats: 83 lines in 2 files changed: 82 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4572.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4572/head:pull/4572

PR: https://git.openjdk.java.net/jdk/pull/4572