Dont panic during actions in the filtered stash view w/o items

Filterng down the stash to 0 items (no cursor is displayed as there are no items
left) caused a panic during execution of one of these actions:
- x: Delete
- m: Set Memo
- s: Stash file

This change prevents that from happening by breaking the switch statement when
there are no items left.
Also glow now uses the filtered markdown notes in the `stashHelpView` so
`m.selectedMarkdown()` cannot return a nil refernce anymore.

ui/stash.go

@@ -505,6 +505,10 @@ func stashUpdate(msg tea.Msg, m stashModel) (stashModel, tea.Cmd) {
 			case "m":
 				m.hideStatusMessage()
 
+				if pages == 0 {
+					break
+				}
+
 				md := m.selectedMarkdown()
 				isUserMarkdown := md.markdownType == stashedMarkdown || md.markdownType == convertedMarkdown
 				isSettingNote := m.state == stashStateSettingNote
@@ -523,6 +527,10 @@ func stashUpdate(msg tea.Msg, m stashModel) (stashModel, tea.Cmd) {
 					break
 				}
 
+				if pages == 0 {
+					break
+				}
+
 				md := m.selectedMarkdown()
 
 				// is the file in the process of being stashed?
@@ -553,6 +561,10 @@ func stashUpdate(msg tea.Msg, m stashModel) (stashModel, tea.Cmd) {
 			case "x":
 				m.hideStatusMessage()
 
+				if pages == 0 {
+					break
+				}
+
 				t := m.selectedMarkdown().markdownType
 				isUserMarkdown := t == stashedMarkdown || t == convertedMarkdown
 				isValidState := m.state != stashStateSettingNote
@@ -933,7 +945,7 @@ func stashHelpView(m stashModel) string {
 		isLocal   bool
 	)
 
-	if len(m.markdowns) > 0 {
+	if len(m.getNotes()) > 0 {
 		md := m.selectedMarkdown()
 		isStashed = md != nil && md.markdownType == stashedMarkdown
 		isLocal = md != nil && md.markdownType == localMarkdown