Fixed "conceptual" bug in 'luaK_setreturns'

This function was computing invalid instruction addresses when the
expression was not a multi-return instruction. (Virtually all machines
don't raise errors when computing an invalid address, as long as the
address is not accessed, but this computation is undefined behavior in
ISO C.)

lcode.c

@@ -703,19 +703,18 @@ static void const2exp (TValue *v, expdesc *e) {
 
 /*
 ** Fix an expression to return the number of results 'nresults'.
-** Either 'e' is a multi-ret expression (function call or vararg)
-** or 'nresults' is LUA_MULTRET (as any expression can satisfy that).
+** 'e' must be a multi-ret expression (function call or vararg).
 */
 void luaK_setreturns (FuncState *fs, expdesc *e, int nresults) {
   Instruction *pc = &getinstruction(fs, e);
   if (e->k == VCALL)  /* expression is an open function call? */
     SETARG_C(*pc, nresults + 1);
-  else if (e->k == VVARARG) {
+  else {
+    lua_assert(e->k == VVARARG);
     SETARG_C(*pc, nresults + 1);
     SETARG_A(*pc, fs->freereg);
     luaK_reserveregs(fs, 1);
   }
-  else lua_assert(nresults == LUA_MULTRET);
 }
 
 

lparser.c

@@ -1014,7 +1014,8 @@ static void funcargs (LexState *ls, expdesc *f, int line) {
         args.k = VVOID;
       else {
         explist(ls, &args);
-        luaK_setmultret(fs, &args);
+        if (hasmultret(args.k))
+          luaK_setmultret(fs, &args);
       }
       check_match(ls, ')', '(', line);
       break;