RFR: 8351653: Webkit debug build failure after update to 620.1

[Jay Bhaskar]

issue : build fails on debug mode. invalid casting
Solution: the casting should be with char* , need to use SourceUTF8().data()

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Commit messages:
 - 8351653: Webkit debug build failure after update to 620.1

Changes: https://git.openjdk.org/jfx/pull/1732/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1732&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8351653
  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jfx/pull/1732.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1732/head:pull/1732

PR: https://git.openjdk.org/jfx/pull/1732