[SPARK-29494][SQL] Fix for ArrayOutofBoundsException while converting string to timestamp

### What changes were proposed in this pull request?
* Adding an additional check in `stringToTimestamp` to handle cases where the input has trailing ':'
* Added a test to make sure this works.

### Why are the changes needed?
In a couple of scenarios while converting from String to Timestamp `DateTimeUtils.stringToTimestamp` throws an array out of bounds exception if there is trailing  ':'. The behavior of this method requires it to return `None` in case the format of the string is incorrect.

### Does this PR introduce any user-facing change?
No

### How was this patch tested?
Added a test in the `DateTimeTestUtils` suite to test if my fix works.

Closes #26143 from rahulsmahadev/SPARK-29494.

Lead-authored-by: Rahul Mahadev <rahul.mahadev@databricks.com>
Co-authored-by: Rahul Shivu Mahadev <51690557+rahulsmahadev@users.noreply.github.com>
Signed-off-by: Sean Owen <sean.owen@databricks.com>

Author: rahulsmahadev

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/util/DateTimeUtils.scala

@@ -286,7 +286,7 @@ object DateTimeUtils {
             i += 1
           }
         } else {
-          if (b == ':' || b == ' ') {
+          if (i < segments.length && (b == ':' || b == ' ')) {
             segments(i) = currentSegmentValue
             currentSegmentValue = 0
             i += 1

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/util/DateTimeUtilsSuite.scala

@@ -456,6 +456,12 @@ class DateTimeUtilsSuite extends SparkFunSuite with Matchers {
     }
   }
 
+  test("trailing characters while converting string to timestamp") {
+    val s = UTF8String.fromString("2019-10-31T10:59:23Z:::")
+    val time = DateTimeUtils.stringToTimestamp(s, defaultZoneId)
+    assert(time == None)
+  }
+
   test("truncTimestamp") {
     def testTrunc(
         level: Int,