Reject a malformed catch clause with a clean error in both modes

jolt's catch is (catch class binding body*); the binding (3rd element) must be
a symbol. Neither the analyzer nor the interpreter validated it, so a non-symbol
binding crashed with an internal Janet error (expected integer key for array...)
and, in the interpreter, a malformed clause whose body never threw was silently
swallowed (returned the try value). Clojure rejects a non-class/non-symbol catch
clause; match that with an up-front error in analyze-try and eval-try.

Surfaced building the Chez try/throw emit. Regression rows in exceptions-spec
(runs x3 modes) plus a unit test asserting the clean message in interpret and
compile. jolt-kg6p.

jolt-core/jolt/analyzer.clj

@@ -162,6 +162,12 @@
         (cond
           (= hname "catch")
             (let [cl (vec (form-elements c))]
+              ;; (catch class binding body*) — binding (3rd elem) MUST be a symbol.
+              ;; Validate eagerly (plain throw, NOT uncompilable, so it's a real
+              ;; error rather than a compile->interpret punt) instead of letting
+              ;; form-sym-name crash on a non-symbol.
+              (when (or (< (count cl) 3) (not (form-sym? (nth cl 2))))
+                (throw "Unable to parse catch clause; expected (catch class binding body*)"))
               (reset! catch-sym (form-sym-name (nth cl 2)))
               (reset! catch-body (drop 3 cl)))
           (= hname "finally")