Remove cname duplication from exc_inspect().

src/error.c

@@ -166,13 +166,10 @@ exc_inspect(mrb_state *mrb, mrb_value exc)
   else {
     const char *cname = mrb_obj_classname(mrb, exc);
     str = mrb_str_new_cstr(mrb, cname);
-    mrb_str_cat_lit(mrb, str, ": ");
     if (append_mesg) {
+      mrb_str_cat_lit(mrb, str, ": ");
       mrb_str_cat_str(mrb, str, mesg);
     }
-    else {
-      mrb_str_cat_cstr(mrb, str, cname);
-    }
   }
   return str;
 }

test/t/exception.rb

@@ -353,7 +353,7 @@ assert('Exception 19') do
 end
 
 assert('Exception#inspect without message') do
-  assert_equal "Exception: Exception", Exception.new.inspect
+  assert_equal "Exception", Exception.new.inspect
 end
 
 assert('Exception#backtrace') do