Show encryption for historical messages

Refactor getting char, introduce get_show_char() to follow DRY principle.

In theory, performance might be negatively affected after this change.

Ideally get_show_char should be optimized in the future.

src/ui/window.h

@@ -98,4 +98,6 @@ void win_remove_entry_message(ProfWin* window, const char* const id);
 
 char* win_quote_autocomplete(ProfWin* window, const char* const input, gboolean previous);
 
+char* get_show_char(prof_enc_t encryption_mode);
+
 #endif