don't go into file select menu when mounting external storage fails

Change-Id: If0efeddc28e1dbb52d9e52abf53323e2cc97c8f0
diff --git a/recovery.c b/recovery.c
index a0df165..40e79d7 100644
--- a/recovery.c
+++ b/recovery.c
@@ -479,7 +479,10 @@
     // Mount the sdcard when the package selection menu is enabled so
     // you can "adb push" packages to the sdcard and immediately
     // install them.
-    ensure_root_path_mounted(EXT_ROOT);
+    if (ensure_root_path_mounted(EXT_ROOT) < 0) {
+        ui_print("Failed to mount external storage.\n");
+        return INSTALL_ERROR;
+    }
 
     const char* MENU_HEADERS[] = { "Choose a package to install:",
                                    root_path,