Fix JRUBY-6324: `pollAndGetClass': java.lang.NullPointerException

The problem here was that srand's global seed was not initialized
at boot, resulting in the first call returning null. That null
propagated into Ruby execution, eventually blowing up in a call
site.

My fix is to make an initial call to the srand logic, creating a
first seed.

src/org/jruby/Ruby.java

@@ -1179,10 +1179,6 @@ private void initCore() {
 
         encodingService = new EncodingService(this);
 
-        if (is1_9()) {
-            RubyRandom.createRandomClass(this);
-        }
-
         RubySymbol.createSymbolClass(this);
 
         if (profile.allowClass("ThreadGroup")) {
@@ -1300,6 +1296,10 @@ private void initCore() {
         if (profile.allowClass("Continuation")) {
             RubyContinuation.createContinuation(this);
         }
+
+        if (is1_9()) {
+            RubyRandom.createRandomClass(this);
+        }
     }
 
     public static final int NIL_PREFILLED_ARRAY_SIZE = RubyArray.ARRAY_DEFAULT_SIZE * 8;

src/org/jruby/RubyRandom.java

@@ -56,6 +56,10 @@ public static RubyClass createRandomClass(Ruby runtime) {
         runtime.setRandomClass(randomClass);
 
         randomClass.defineAnnotatedMethods(RubyRandom.class);
+
+        // initialize the global seed by triggering an iteration
+        srandCommon(runtime.getCurrentContext(), randomClass, runtime.getNil(), false);
+
         return randomClass;
     }