Integrated: 8261705: Swing jtreg tests fail Metal API Validation with missing buffer binding

[Jayathirth D V]

We are hitting MTLRenderer_DrawScanLine with scanlineCount=0. So we end up calling drawPrimitives without actual vertex data. This is causing error when Metal API Validation is enabled. In OpenGL we have null checks for scanline data as well as scanlinecount. We need similar check in case of Metal.

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Commit messages:
 - 8261705: Swing jtreg tests fail Metal API Validation with missing buffer binding

Changes: https://git.openjdk.java.net/lanai/pull/191/files
 Webrev: https://webrevs.openjdk.java.net/?repo=lanai&pr=191&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8261705
  Stats: 9 lines in 1 file changed: 5 ins; 4 del; 0 mod
  Patch: https://git.openjdk.java.net/lanai/pull/191.diff
  Fetch: git fetch https://git.openjdk.java.net/lanai pull/191/head:pull/191

PR: https://git.openjdk.java.net/lanai/pull/191