RFR: 8287609: Add null-check for tagsArray returned from CTFontCopyAvailableTables

[Nikita Gubarkov]

`CTFontCopyAvailableTables` can return null, which causes subsequent call to `CFArrayGetCount` to crash with SEGFAULT, just added a null-check.

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Commit messages:
 - 8287609: Add null-check for tagsArray returned from CTFontCopyAvailableTables

Changes: https://git.openjdk.java.net/jdk/pull/8962/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8962&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8287609
  Stats: 3 lines in 1 file changed: 3 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8962.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8962/head:pull/8962

PR: https://git.openjdk.java.net/jdk/pull/8962