RFR: 8282548: Create a regression test for JDK-4330998

[Manukumar V S]

Create a regression test for [JDK-4330998](https://bugs.openjdk.java.net/browse/JDK-4330998)

Issue tested:
When calling JEditorPane.setText(null), the following exception is thrown:

java.lang.NullPointerException:
        at java.io.StringReader.<init>(StringReader.java:38)

Testing:
Java 1.4.0 -> Test Failed.
$ ./j2sdk1.4.0/bin/java bug4330998Win
java.lang.RuntimeException: Test failed, caught Exception java.lang.NullPointerException when calling text.setText(null)
        at bug4330998Win.runTest(bug4330998Win.java:45)
        at bug4330998Win.main(bug4330998Win.java:51)
Exception in thread "main"

Java 1.4.1 -> Test Passed.
$ ./j2sdk1.4.1/bin/java bug4330998Win
Test passed

-------------

Commit messages:
 - 8282548: Create a regression test for JDK-4330998

Changes: https://git.openjdk.java.net/jdk/pull/7740/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7740&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8282548
  Stats: 55 lines in 1 file changed: 55 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7740.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7740/head:pull/7740

PR: https://git.openjdk.java.net/jdk/pull/7740