tiff: print log in case of unknown / unsupported tag

Helps debugging.

libavcodec/tiff.c

@@ -474,6 +474,9 @@ static int tiff_decode_tag(TiffContext *s, const uint8_t *start, const uint8_t *
         if(s->compr == TIFF_G4)
             s->fax_opts = value;
         break;
+
+    default:
+        av_log(s->avctx, AV_LOG_DEBUG, "Unknown or unsupported tag %d/0X%0X\n", tag, tag);
     }
     return 0;
 }