Added comment

src/libImaging/TiffDecode.c

@@ -720,9 +720,14 @@ ImagingLibTiffDecode(
     }
 
  decode_err:
+    // TIFFClose in libtiff calls tif_closeproc and TIFFCleanup
     if (clientstate->fp) {
+        // Pillow will manage the closing of the file rather than libtiff
+        // So only call TIFFCleanup
         TIFFCleanup(tiff);
     } else {
+        // When tif_closeproc refers to our custom _tiffCloseProc though,
+        // that is fine, as it does not close the file
         TIFFClose(tiff);
     }
     TRACE(("Done Decoding, Returning \n"));