Skip spaces early so we don't consume more tokens

Several new unpack specs were failing because they did not raise
an error for directives like "a 0A". The problem was that because
the handling of the space occurred in the main switch for unpack,
it also caused the "0" to be consumed as an unused occurrence
count. The unpack then proceeded on to the "A" and returned a
result rather than raising.

This change matches CRuby by moving the space check all the way to
the top of the loop, so that spaces are skipped without any
further processing of the next element in the directive.

core/src/main/java/org/jruby/util/Pack.java

@@ -982,7 +982,9 @@ private static IRubyObject unpackInternal(ThreadContext context, RubyString enco
         mainLoop: while (next != 0) {
             int type = next;
             next = getDirective(context, "unpack", formatString, format);
-
+
+            if (isSpace(type)) continue;
+
             if (type == '#') {
                 while (type != '\n') {
                     if (next == 0) break mainLoop;
@@ -1094,13 +1096,6 @@ private static IRubyObject unpackInternal(ThreadContext context, RubyString enco
                 case 'w':
                     value = unpack_w(context, block, result, encode, occurrences, mode);
                     break;
-                case ' ':       // various "ok" whitespace
-                case '\011':
-                case '\n':
-                case '\013':
-                case '\014':
-                case '\015':
-                    break;
                 default:
                     unknownDirective(context, "unpack", type, formatString);
                     break;
@@ -1111,6 +1106,15 @@ private static IRubyObject unpackInternal(ThreadContext context, RubyString enco
         return result;
     }
 
+    private static boolean isSpace(int type) {
+        boolean isSpace = switch (type) {
+            case ' ', '\011', '\n', '\013', '\014', '\015' -> true;
+            default -> false;
+        };
+        if (isSpace) return true;
+        return false;
+    }
+
     private static IRubyObject unpack_w(ThreadContext context, Block block, RubyArray result, ByteBuffer encode, int occurrences, int mode) {
         if (occurrences == IS_STAR || occurrences > encode.remaining()) {
             occurrences = encode.remaining();