6513803: httpserver regression test Test13 failing and causing NullPointerException

Check for NPEs

Reviewed-by: chegar

jdk/test/com/sun/net/httpserver/Test1.java

@@ -86,8 +86,11 @@ public class Test1 extends Test {
             System.out.println ("OK");
         } finally {
             delay();
+            if (s1 != null)
                 s1.stop(2);
+            if (s2 != null)
                 s2.stop(2);
+            if (executor != null)
                 executor.shutdown ();
         }
     }

jdk/test/com/sun/net/httpserver/Test12.java

@@ -85,8 +85,11 @@ public class Test12 extends Test {
             System.out.println ("OK");
         } finally {
             delay();
+            if (s1 != null)
                 s1.stop(2);
+            if (s2 != null)
                 s2.stop(2);
+            if (executor != null)
                 executor.shutdown ();
         }
     }

jdk/test/com/sun/net/httpserver/Test13.java

@@ -81,8 +81,11 @@ public class Test13 extends Test {
             System.out.println ("OK");
         } finally {
             delay();
+            if (s1 != null)
                 s1.stop(2);
+            if (s2 != null)
                 s2.stop(2);
+            if (executor != null)
                 executor.shutdown ();
         }
     }

jdk/test/com/sun/net/httpserver/Test3.java

@@ -62,7 +62,9 @@ public class Test3 extends Test {
             System.out.println ("OK");
         } finally {
             delay();
+            if (server != null)
                 server.stop(2);
+            if (exec != null)
                 exec.shutdown();
         }
     }

jdk/test/com/sun/net/httpserver/Test4.java

@@ -60,7 +60,9 @@ public class Test4 extends Test {
             System.out.println ("OK");
         } finally {
             delay();
+            if (server != null)
                 server.stop(2);
+            if (exec != null)
                 exec.shutdown();
         }
     }

jdk/test/com/sun/net/httpserver/Test5.java

@@ -61,7 +61,9 @@ public class Test5 extends Test {
             System.out.println ("OK");
         } finally {
             delay ();
+            if (server != null)
                 server.stop(2);
+            if (exec != null)
                 exec.shutdown();
         }
     }

jdk/test/com/sun/net/httpserver/Test9.java

@@ -97,8 +97,11 @@ public class Test9 extends Test {
             System.out.println ("OK");
         } finally {
             delay();
+            if (s1 != null)
                 s1.stop(2);
+            if (s2 != null)
                 s2.stop(2);
+            if (executor != null)
                 executor.shutdown ();
         }
     }

jdk/test/com/sun/net/httpserver/Test9a.java

@@ -92,7 +92,9 @@ public class Test9a extends Test {
             System.out.println ("OK");
         } finally {
             delay();
+            if (server != null)
                 server.stop(2);
+            if (executor != null)
                 executor.shutdown();
         }
     }

jdk/test/com/sun/net/httpserver/TestLogging.java

@@ -89,7 +89,9 @@ public class TestLogging extends Test {
             System.out.println ("OK");
         } finally {
             delay();
+            if (s1 != null)
                 s1.stop(2);
+            if (executor != null)
                 executor.shutdown();
         }
     }