FlipperHTTP: Fix wrong return type warning

flip_library/flipper_http.h

@@ -230,7 +230,7 @@ FuriString* flipper_http_load_from_file(char* file_path) {
         storage_file_close(file);
         storage_file_free(file);
         furi_record_close(RECORD_STORAGE);
-        return false;
+        return NULL;
     }
 
     // Append each byte to the FuriString

flip_weather/flipper_http.h

@@ -230,7 +230,7 @@ FuriString* flipper_http_load_from_file(char* file_path) {
         storage_file_close(file);
         storage_file_free(file);
         furi_record_close(RECORD_STORAGE);
-        return false;
+        return NULL;
     }
 
     // Append each byte to the FuriString

flip_wifi/flip_wifi_i.h

@@ -195,7 +195,7 @@ static FlipWiFiApp* flip_wifi_app_alloc() {
            callback_to_submenu_saved,
            &app->view_dispatcher,
            app)) {
-        return false;
+        return NULL;
     }
 
     // Load the playlist from storage