screenshot: only strip ext from basename

Since the filename property returns URLs unchanged `stripext` needs to
establish the basename itself. This fixes an issue with the new behavior
where `%F` in a screenshot template could have resulted in stripping
beyond the top level domain, in case there were no dots after it.

Author: WhitePeter

player/screenshot.c

@@ -70,7 +70,7 @@ void screenshot_init(struct MPContext *mpctx)
 
 static char *stripext(void *talloc_ctx, const char *s)
 {
-    const char *end = strrchr(s, '.');
+    const char *end = strrchr(mp_basename(s), '.');
     if (!end)
         end = s + strlen(s);
     return talloc_asprintf(talloc_ctx, "%.*s", (int)(end - s), s);