Fixed compiler warnings on Visual Studio 2013

src/file/SDL_rwops.c

@@ -676,13 +676,13 @@ SDL_LoadFile_RW(SDL_RWops * src, size_t *datasize, int freesrc)
     if (size < 0) {
         size = FILE_CHUNK_SIZE;
     }
-    data = SDL_malloc(size+1);
+    data = SDL_malloc((size_t)(size + 1));
 
     size_total = 0;
     for (;;) {
         if ((size_total + FILE_CHUNK_SIZE) > size) {
             size = (size_total + FILE_CHUNK_SIZE);
-            newdata = SDL_realloc(data, size + 1);
+            newdata = SDL_realloc(data, (size_t)(size + 1));
             if (!newdata) {
                 SDL_free(data);
                 data = NULL;

src/joystick/SDL_gamecontroller.c

@@ -142,13 +142,13 @@ SDL_LoadVIDPIDListFromHint(const char *hint, SDL_vidpid_list *list)
     }
 
     while ((spot = SDL_strstr(spot, "0x")) != NULL) {
-        entry = SDL_strtol(spot, &spot, 0);
+        entry = (Uint16)SDL_strtol(spot, &spot, 0);
         entry <<= 16;
         spot = SDL_strstr(spot, "0x");
         if (!spot) {
             break;
         }
-        entry |= SDL_strtol(spot, &spot, 0);
+        entry |= (Uint16)SDL_strtol(spot, &spot, 0);
 
         if (list->num_entries == list->max_entries) {
             int max_entries = list->max_entries + 16;

src/video/windows/SDL_windowsmessagebox.c

@@ -346,7 +346,6 @@ WIN_ShowMessageBox(const SDL_MessageBoxData *messageboxdata, int *buttonid)
 {
     WIN_DialogData *dialog;
     int i, x, y;
-    UINT_PTR which;
     const SDL_MessageBoxButtonData *buttons = messageboxdata->buttons;
     HFONT DialogFont;
     SIZE Size;