Improve _get_comp_words_by_ref()

Empty $cur when cmd = "|a " (| = cursor position)

bash_completion

@@ -348,9 +348,10 @@ __get_cword_at_cursor_by_ref()
     local cword words=()
     __reassemble_comp_words_by_ref "$1" words cword
 
-    local i cur2
-    local cur="$COMP_LINE"
-    local index="$COMP_POINT"
+    local i cur cur2
+    local index=$COMP_POINT
+    if (( index )); then
+        cur=$COMP_LINE
         for (( i = 0; i <= cword; ++i )); do
             while [[
                 # Current word fits in $cur?
@@ -373,6 +374,7 @@ __get_cword_at_cursor_by_ref()
                 index=$(( index - old_size + new_size ))
             fi
         done
+    fi
 
     if [[ $index -lt 0 ]]; then
         # This happens when completing: "command | arg" (| is where