Fix condition-case empty success handler misinterpretation

(condition-case X E (:success)) should return nil; the compiler
behaves correctly in this case.

* src/eval.c (internal_lisp_condition_case):
Evaluate an empty :success handler as nil instead of pretending it
isn't there.
* test/lisp/emacs-lisp/bytecomp-tests.el (bytecomp-tests--test-cases):
Add test case.

test/lisp/emacs-lisp/bytecomp-tests.el

@@ -752,6 +752,11 @@ inner loops respectively."
       (condition-case nil
           (characterp x)               ; value (no :success, no var)
         (error 'bad)))
+
+    (condition-case nil
+        (bytecomp-test-identity 3)
+      (error 'bad)
+      (:success))                       ; empty handler
     )
   "List of expressions for cross-testing interpreted and compiled code.")