Dump non-ASCII char as unsigned

Non-ASCII code may be negative on platforms plain char is signed.

ext/objspace/objspace_dump.c

@@ -142,7 +142,7 @@ dump_append_sizet(struct dump_config *dc, const size_t number)
 }
 
 static void
-dump_append_c(struct dump_config *dc, char c)
+dump_append_c(struct dump_config *dc, unsigned char c)
 {
     if (c <= 0x1f) {
         const unsigned int width = (sizeof(c) * CHAR_BIT / 4) + 5;

test/objspace/test_objspace.rb

@@ -725,4 +725,19 @@ class TestObjSpace < Test::Unit::TestCase
       assert_equal '42', out[2]
     end
   end
+
+  def test_utf8_method_names
+    name = "utf8_❨╯°□°❩╯︵┻━┻"
+    obj = ObjectSpace.trace_object_allocations do
+      __send__(name)
+    end
+    dump = ObjectSpace.dump(obj)
+    assert_equal name, JSON.parse(dump)["method"], dump
+  end
+
+  private
+
+  def utf8_❨╯°□°❩╯︵┻━┻
+    "1#{2}"
+  end
 end