fix PATCH_DIR is nil

Author: debugly

README.md

@@ -1,6 +1,6 @@
 ## MRFFToolChain Build Shell
 
-![](https://img.shields.io/github/downloads/debugly/MRFFToolChainBuildShell/total) <img src="https://img.shields.io/badge/Platform-%20iOS%20macOS%20tvOS%20Android-blue.svg">
+![](https://img.shields.io/github/downloads/debugly/MRFFToolChainBuildShell/total) <img src="https://img.shields.io/badge/Platform-%20iOS%20macOS%20tvOS%20Android-blue.svg"><img src="https://img.shields.io/badge/FFmpeg-%207.1.1%20-blue.svg"><img src="https://img.shields.io/badge/FFmpeg-%206.1.1%20-blue.svg"><img src="https://img.shields.io/badge/FFmpeg-%205.1.6%20-blue.svg"><img src="https://img.shields.io/badge/FFmpeg-%204.0.5%20-blue.svg">
 
 **What's MRFFToolChain?**
 

do-init/init-repo.sh

@@ -71,6 +71,11 @@ function apply_patches() {
         return
     fi
 
+    if [[ -z "$PATCH_DIR" ]]; then
+        echo "$REPO_DIR hasn't any patch"
+        return
+    fi
+
     local plat="$MR_PLAT"
     local patch_dir="${THIS_DIR}/../patches/$PATCH_DIR"