Integrated: 8261908: DrawScanline vertex calculation is not proper

[Jayathirth D V]

After JDK-8261706 we have wrong vertex calculation in DrawScanline when total vertex data is < 4096 and it causes artifacts in RenderPerfTest with uiScale=1.0. Corrected the vertex count calculation.

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Commit messages:
 - 8261908: DrawScanline vertex calculation is not proper

Changes: https://git.openjdk.java.net/lanai/pull/195/files
 Webrev: https://webrevs.openjdk.java.net/?repo=lanai&pr=195&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8261908
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/lanai/pull/195.diff
  Fetch: git fetch https://git.openjdk.java.net/lanai pull/195/head:pull/195

PR: https://git.openjdk.java.net/lanai/pull/195