Refactor: Quote files passed to preview functions

In some cases we need to pass multiple files to preview functions. These
files are treated as a single string that is evaluated by fzf and passed
on to our preview functions as individual arguments.
This commit introduces a _forgit_quote_files function that ensures the
resulting arguments are quoted properly.

bin/git-forgit

@@ -104,6 +104,29 @@ _forgit_parse_array() {
     ${old_IFS+"false"} && unset IFS || IFS="$old_IFS"
 }
 
+# parse the input arguments and print only those after the "--"
+# separator as a single line of quoted arguments to stdout
+_forgit_quote_files() {
+    local files add
+    files=()
+    add=false
+    while (( "$#" )); do
+        case "$1" in
+            --)
+            add=true
+            shift
+            ;;
+            *)
+            if [ $add == true ]; then
+                files+=("'$1'")
+            fi
+            shift
+            ;;
+        esac
+    done
+    echo "${files[*]}"
+}
+
 _forgit_pager=${FORGIT_PAGER:-$(git config core.pager || echo 'cat')}
 _forgit_show_pager=${FORGIT_SHOW_PAGER:-$(git config pager.show || echo "$_forgit_pager")}
 _forgit_diff_pager=${FORGIT_DIFF_PAGER:-$(git config pager.diff || echo "$_forgit_pager")}
@@ -138,14 +161,14 @@ _forgit_log_enter() {
 # git commit viewer
 _forgit_log() {
     _forgit_inside_work_tree || return 1
-    local opts graph files log_format
-    files=$(sed -nE 's/.*-- (.*)/\1/p' <<< "$*") # extract files parameters for `git show` command
+    local opts graph quoted_files log_format
+    quoted_files=$(_forgit_quote_files "$@")
     opts="
         $FORGIT_FZF_DEFAULT_OPTS
         +s +m --tiebreak=index
-        --bind=\"enter:execute($FORGIT log_enter {} $files)\"
+        --bind=\"enter:execute($FORGIT log_enter {} $quoted_files)\"
         --bind=\"ctrl-y:execute-silent($FORGIT yank_sha {})\"
-        --preview=\"$FORGIT log_preview {} $files\"
+        --preview=\"$FORGIT log_preview {} $quoted_files\"
         $FORGIT_LOG_FZF_OPTS
     "
     graph=()
@@ -532,17 +555,17 @@ _forgit_cherry_pick_from_branch() {
 
 _forgit_rebase() {
     _forgit_inside_work_tree || return 1
-    local opts graph files target_commit prev_commit
+    local opts graph quoted_files target_commit prev_commit
     graph=()
     [[ $_forgit_log_graph_enable == true ]] && graph=(--graph)
     _forgit_rebase_git_opts=()
     _forgit_parse_array _forgit_rebase_git_opts "$FORGIT_REBASE_GIT_OPTS"
-    files=$(sed -nE 's/.* -- (.*)/\1/p' <<< "$*") # extract files parameters for `git show` command
+    quoted_files=$(_forgit_quote_files "$@")
     opts="
         $FORGIT_FZF_DEFAULT_OPTS
         +s +m --tiebreak=index
         --bind=\"ctrl-y:execute-silent($FORGIT yank_sha {})\"
-        --preview=\"$FORGIT file_preview {} $files\"
+        --preview=\"$FORGIT file_preview {} $quoted_files\"
         $FORGIT_REBASE_FZF_OPTS
     "
     target_commit=$(
@@ -566,17 +589,17 @@ _forgit_file_preview() {
 _forgit_fixup() {
     _forgit_inside_work_tree || return 1
     git diff --cached --quiet && echo 'Nothing to fixup: there are no staged changes.' && return 1
-    local opts graph files target_commit prev_commit
+    local opts graph quoted_files target_commit prev_commit
     graph=()
     [[ $_forgit_log_graph_enable == true ]] && graph=(--graph)
     _forgit_fixup_git_opts=()
     _forgit_parse_array _forgit_fixup_git_opts "$FORGIT_FIXUP_GIT_OPTS"
-    files=$(sed -nE 's/.* -- (.*)/\1/p' <<< "$*")
+    quoted_files=$(_forgit_quote_files "$@")
     opts="
         $FORGIT_FZF_DEFAULT_OPTS
         +s +m --tiebreak=index
         --bind=\"ctrl-y:execute-silent($FORGIT yank_sha {})\"
-        --preview=\"$FORGIT file_preview {} $files\"
+        --preview=\"$FORGIT file_preview {} $quoted_files\"
         $FORGIT_FIXUP_FZF_OPTS
     "
     target_commit=$(