RFR: 8314141: Missing default for switch in CreateBitmap

[Ambarish Rapte]

This is a simple change to add a missing default statement.
@kevinrushforth @jayathirthrao please review.

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Commit messages:
 - default: return NULL;

Changes: https://git.openjdk.org/jfx/pull/1206/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1206&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8314141
  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jfx/pull/1206.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1206/head:pull/1206

PR: https://git.openjdk.org/jfx/pull/1206