cat-highlight: Fix infinite loop, check if $LESSOPEN is set

.config/zsh/functions.zsh

@@ -31,11 +31,12 @@ function export-emacs
 # Highlight cat output with whatever less is using for highlighting
 function cat-highlight()
 {
-    if [[ -t 1 ]]; then         # We're in a terminal
+    # Check if we are in a terminal and $LESSOPEN is not empty
+    if [[ -t 1 && -n "${LESSOPEN}" ]]; then
         CATOPEN="${LESSOPEN/| }"
         CATOPEN="${CATOPEN/ %s}"
-        cat $@ | eval ${CATOPEN}
+        \cat $@ | eval ${CATOPEN}
     else
-        cat $@
+        \cat $@
     fi
 }