disable redrawing when setting visible region to prevent flickering

Author: danthe1st

bundles/org.eclipse.jface.text/projection/org/eclipse/jface/text/source/projection/ProjectionViewer.java

@@ -768,6 +768,7 @@ public void setVisibleRegion(int start, int length) {
 			return;
 		}
 		try {
+			setRedraw(false);
 			// If the visible region changes, make sure collapsed regions outside of the old visible regions are expanded
 			// and collapse everything outside the new visible region
 			int end= computeEndOfVisibleRegion(start, length, document);
@@ -782,6 +783,8 @@ public void setVisibleRegion(int start, int length) {
 		} catch (BadLocationException e) {
 			ILog log= ILog.of(getClass());
 			log.log(new Status(IStatus.WARNING, getClass(), IStatus.OK, null, e));
+		} finally {
+			setRedraw(true);
 		}
 	}