Fixed bug of access violation in finalizers

Errors in finalizers need a valid 'pc' to produce an error message,
even if the error is not propagated. Therefore, calls to the GC (which
may call finalizers) inside luaV_execute must save the 'pc'.

lvm.c

@@ -1101,9 +1101,9 @@ void luaV_finishOp (lua_State *L) {
 /* idem, but without changing the stack */
 #define halfProtectNT(exp)  (savepc(L), (exp))
 
-
+/* 'c' is the limit of live values in the stack */
 #define checkGC(L,c)  \
-	{ luaC_condGC(L, L->top = (c),  /* limit of live values */ \
+	{ luaC_condGC(L, (savepc(L), L->top = (c)), \
                          updatetrap(ci)); \
            luai_threadyield(L); }
 
@@ -1791,8 +1791,7 @@ void luaV_execute (lua_State *L, CallInfo *ci) {
         vmbreak;
       }
       vmcase(OP_VARARGPREP) {
-        luaT_adjustvarargs(L, GETARG_A(i), ci, cl->p);
-        updatetrap(ci);
+        ProtectNT(luaT_adjustvarargs(L, GETARG_A(i), ci, cl->p));
         if (trap) {
           luaD_hookcall(L, ci);
           L->oldpc = pc + 1;  /* next opcode will be seen as a "new" line */