Bug 575398 - CTabFolderRenderer: fix drawing the cross on Win32

Drawing using default lines causes the red cross close button lopsided
on Win32 non-HiDPI. When round line caps are used, the cross is drawn
correctly.

Change-Id: I87599fa2e893a7bd1f6205e4d8936fdf978ef31d
Signed-off-by: Rolf Theunissen <[email protected]>
Reviewed-on: https://git.eclipse.org/r/c/platform/eclipse.platform.swt/+/185829
Tested-by: Andrey Loskutov <[email protected]>
Reviewed-by: Andrey Loskutov <[email protected]>

Author: rolfth

bundles/org.eclipse.swt/Eclipse SWT Custom Widgets/common/org/eclipse/swt/custom/CTabFolderRenderer.java

@@ -899,6 +899,7 @@ private void drawCloseLines(GC gc, int x, int y, int lineLength, boolean hot) {
 			gc.setLineWidth(gc.getLineWidth() + 2);
 			gc.setForeground(getFillColor());
 		}
+		gc.setLineCap(SWT.CAP_ROUND);
 		gc.drawLine(x, y, x + lineLength, y + lineLength);
 		gc.drawLine(x, y + lineLength, x + lineLength, y);
 	}