Add a redundant intialisation to squash a gcc warning.

execute.c

@@ -168,7 +168,7 @@ jv jq_next(jq_state *jq) {
       dump_operation(frame_current_bytecode(&jq->frame_stk), pc);
       printf("\t");
       const struct opcode_description* opdesc = opcode_describe(opcode);
-      data_stk_elem* param;
+      data_stk_elem* param = 0;
       int stack_in = opdesc->stack_in;
       if (stack_in == -1) stack_in = pc[1];
       for (int i=0; i<stack_in; i++) {