Add get_marker method to dc_array_t

deltachat-ffi/src/dc_array.rs

@@ -39,6 +39,17 @@ impl dc_array_t {
         }
     }
 
+    pub(crate) fn get_marker(&self, index: usize) -> Option<&str> {
+        match self {
+            Self::MsgIds(_) => None,
+            Self::Chat(array) => None,
+            Self::Locations(array) => array
+                .get(index)
+                .and_then(|location| location.marker.as_deref()),
+            Self::Uint(_) => None,
+        }
+    }
+
     pub(crate) fn get_location(&self, index: usize) -> &Location {
         if let Self::Locations(array) = self {
             &array[index]