Fix savestate thumbnails - '.png' needs to be appended to the total

filepath, so fill_pathname can't be used since it would overwrite
the existing extension

tasks/task_screenshot.c

@@ -307,8 +307,13 @@ static bool screenshot_dump(
    if (!fullpath)
    {
       if (savestate)
-         fill_pathname(state->filename,
-               name_base, ".png", sizeof(state->filename));
+      {
+         size_t _len             = strlcpy(state->filename,
+               name_base, sizeof(state->filename));
+         strlcpy(state->filename       + _len,
+               ".png",
+               sizeof(state->filename) - _len);
+      }
       else
       {
          char new_screenshot_dir[DIR_MAX_LENGTH];
@@ -361,9 +366,14 @@ static bool screenshot_dump(
                   IMG_EXT, sizeof(state->shotname));
          }
          else
-            fill_pathname(state->shotname,
-                  path_basename_nocompression(name_base),
-                  ".png", sizeof(state->shotname));
+         {
+            size_t _len = strlcpy(state->shotname,
+                path_basename_nocompression(name_base),
+                 sizeof(state->shotname));
+            strlcpy(state->shotname       + _len,
+                  ".png",
+                  sizeof(state->shotname) - _len);
+         }
 
          if (     string_is_empty(new_screenshot_dir)
                || settings->bools.screenshots_in_content_dir)