Guarded pattern case variable reports an error in error log.

Change-Id: I5b46d997f04624e49cee3b4676f05866aeadf921
Signed-off-by: Vikas Chandra <Vikas.Chandra@in.ibm.com>
Reviewed-on: https://git.eclipse.org/r/c/jdt/eclipse.jdt.core/+/184851
Tested-by: JDT Bot <jdt-bot@eclipse.org>
Reviewed-by: Jay Arthanareeswaran <jarthana@in.ibm.com>