Fixed bug in tail calls of __call chains

A tail call of a __call chain (a __call metamethod that itself is
also not a function) was being perfomed as a regular call.

lvm.c

@@ -1549,9 +1549,10 @@ void luaV_execute (lua_State *L, CallInfo *ci) {
           luaF_close(L, base, NOCLOSINGMETH);
           lua_assert(base == ci->func + 1);
         }
-        if (!ttisfunction(s2v(ra))) {  /* not a function? */
+        while (!ttisfunction(s2v(ra))) {  /* not a function? */
           luaD_tryfuncTM(L, ra);  /* try '__call' metamethod */
           b++;  /* there is now one extra argument */
+          checkstackp(L, 1, ra);
         }
         if (!ttisLclosure(s2v(ra))) {  /* C function? */
           luaD_call(L, ra, LUA_MULTRET);  /* call it */