preview-kitty: fix crash on first file on dash (#636)

In the dash shell, when `exec < fifo` is interrupted by SIGCHLD, it exits.
So we replace it with `cat fifo |`.

Issue discussed in #614

plugins/preview-kitty

@@ -63,7 +63,9 @@ if [ "$PREVIEW_MODE" ] ; then
 
     preview_file "$1"
 
-    exec < "$NNN_FIFO"
+    # use cat instead of 'exec <' to avoid issues with dash shell
+    # shellcheck disable=SC2002
+    cat "$NNN_FIFO" |\
     while read -r selection ; do
         preview_file "$selection"
     done