cdfs: fix createdvd CHD hashing for PS2/PSP RetroAchievements (#18955)

DVD-format CHDs created with `chdman createdvd` have no CD track
metadata. The DVD metadata tag sets track type to "DVD" but leaves
frames=0, causing chdstream_find_special_track to skip the track
when selecting CHDSTREAM_TRACK_PRIMARY since 0 > 0 is false.

Fix by immediately returning DVD tracks as the primary data track,
since a createdvd CHD only ever has one track and it is always data.

Fixes hash generation failed for PS2/PSP games stored as createdvd
CHDs when using RetroAchievements. Closes #16145.

Author: lazepeda01

libretro-common/streams/chd_stream.c

@@ -320,6 +320,13 @@ chdstream_find_special_track(chd_file *fd, int32_t track, metadata_t *meta)
             }
             break;
          case CHDSTREAM_TRACK_PRIMARY:
+            /* DVD tracks have no frame count in metadata but are always
+             * the primary data track - select immediately */
+            if (strcmp(iter.type, "DVD") == 0)
+            {
+               *meta = iter;
+               return true;
+            }
             if (strcmp(iter.type, "AUDIO") && iter.frames > largest_size)
             {
                largest_size  = iter.frames;