Launcher: No longer include ROM extension in PNG filenames

Before: `/roms/nes/Super Mario.nes` => `/covers/nes/Super Mario.nes.png`

Now: `/roms/nes/Super Mario.nes` => `/covers/nes/Super Mario.png`

The change is mainly made to accommodate support for zip files.

But this is also how other emulation frontends name their art by default, as well as tools like Skraper.

This is a breaking change but filename-based art was only recently advertised so few people should be using it. (We could also check for the old format, but sd card access is very slow and I don't think it's worth the few ms it would add for everybody).

README.md

@@ -66,7 +66,7 @@ This method is intended to be used when .fw support isn't available (when portin
 Game covers should be placed in the `romart` folder at the base of your sd card. You can obtain a pre-made pack [here](https://github.com/ducalex/retro-go-covers). Retro-Go is also compatible with the older Go-Play romart pack.
 
 You can add missing cover art by creating a PNG image (160x168, 8bit). Two naming schemes are supported:
-- Filename-based: `/romart/nes/Super Mario.nes.png` (notice the rom extension is included)
+- Filename-based: `/romart/nes/Super Mario.png` (notice the rom extension is *not* included)
 - CRC32-based: `/romart/nes/A/ABCDE123.png` where `nes` is the same as the rom folder, and `ABCDE123` is the CRC32 of the game (press A -> Properties in the launcher to find it), and `A` is the first character of the CRC32
 
 _Note: CRC32-based, which is what is used in the pre-made pack, is much slower than name-based! This type is useful because filenames vary greatly despite having identical CRCs, but if you generate your own art I suggest you use filename-based format and delete all CRC-based art from your SD Card to improve responsiveness._

launcher/main/gui.c

@@ -575,7 +575,11 @@ void gui_load_preview(tab_t *tab)
         else if (type == 0x2 && app->use_crc_covers && application_get_file_crc32(file)) // Game cover (png)
             path_len = snprintf(path, RG_PATH_MAX, "%s/%X/%08X.png", app->paths.covers, (int)(file->checksum >> 28), (int)file->checksum);
         else if (type == 0x3) // Game cover (based on filename)
-            path_len = snprintf(path, RG_PATH_MAX, "%s/%s.png", app->paths.covers, file->name);
+        {
+            path_len = snprintf(path, RG_PATH_MAX, "%s/%s", app->paths.covers, file->name);
+            if (path_len < RG_PATH_MAX - 3) // Don't bother if we already have an overflow
+                strcpy(path + path_len - strlen(rg_extension(file->name)), "png");
+        }
         else if (type == 0x4) // Save state screenshot (png)
         {
             rg_emu_states_t *savestates = rg_emu_get_states(path, 4);