Fix out-of-bound access in KeySymToUcs4()

Array `keysym_to_unicode_590_5fe` is only valid for range  [0x590, 0x5fe] but current lower-bound is checked against 0x589.
So invalid values from 0x58a to 0x58f are being allowed by current check.

If any of these invalid value is passed as `keysym`,    `keysym - 0x590` would underflow.
4 jobs for gujjwal00-master-patch-74222 in 1 minute and 13 seconds (queued for 1 second)
latest
Status Job ID Name Coverage
  Prep
failed #9607895
check-commits

00:00:45

passed #9607896
container-prep

00:01:12

 
  Build
skipped #9607897
build
 
  Deploy
skipped #9607898
allowed to fail
check-merge-request
 
Name Stage Failure
failed
check-commits Prep
2. Missing "Signed-off-by: author information"
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Uploading artifacts for failed job
Uploading artifacts...
results.xml: found 1 matching files and directories

Uploading artifacts as "junit" to coordinator... ok
id=9607895 responseStatus=201 Created token=3wLCESYB
Cleaning up file based variables
ERROR: Job failed: exit code 1