fix: BrowseDirectors - birthdate sorting when undefined, added comments

frontend/src/components/BrowseDirectors.tsx

@@ -19,7 +19,6 @@ const exampleDirectors: DirectorIO[] = [{
     id: "890",
     name: "Karel",
     surname: "Vomacka",
-    birthdate: "1.2.1987",
   },
   {
     id: "666",
@@ -58,15 +57,18 @@ export const BrowseDirectors = () => {
         const second = b?.birthdate?.split('.').reverse();
 
         if (first === undefined && second === undefined) { return 0; }
-        if (first === undefined) { return 1;}
-        if (second === undefined) { return -1;}
+        if (first === undefined) { return -1;}
+        if (second === undefined) { return 1;}
 
+        // year
         if (first[0] > second[0]) {return 1;}
         if (first[0] < second[0]) {return -1;}
-        
+
+        // month
         if (first[1] > second[1]) {return 1;}
         if (first[1] < second[1]) {return -1;}
-        
+
+        // day
         if (first[2] > second[2]) {return 1;}
         if (first[2] < second[2]) {return -1;}
         return 0;