YJIT: Fix crash when yielding keyword arguments

Previously, the code for dropping surplus arguments when yielding
into blocks erroneously attempted to drop keyword arguments when there
is in fact no surplus arguments. Fix the condition and test that
supplying the exact number of keyword arguments as require compiles
without fallback.

test/ruby/test_yjit.rb

@@ -1742,6 +1742,14 @@ class TestYJIT < Test::Unit::TestCase
     RUBY
   end
 
+  def test_yield_kwargs
+    assert_compiles(<<~RUBY, result: 3, no_send_fallbacks: true)
+      def req2kws = yield a: 1, b: 2
+
+      req2kws { |a:, b:| a + b }
+    RUBY
+  end
+
   private
 
   def code_gc_helpers

yjit/src/codegen.rs

@@ -8011,14 +8011,14 @@ fn gen_send_iseq(
 
     // Pop surplus positional arguments when yielding
     if arg_setup_block {
-        let extras = argc - required_num - opt_num;
+        let extras = argc - required_num - opt_num - kw_arg_num;
         if extras > 0 {
             // Checked earlier. If there are keyword args, then
             // the positional arguments are not at the stack top.
             assert_eq!(0, kw_arg_num);
 
             asm.stack_pop(extras as usize);
-            argc = required_num + opt_num;
+            argc = required_num + opt_num + kw_arg_num;
         }
     }