Fix save image to

app/src/main/java/com/hippo/ehviewer/AppConfig.java

@@ -97,6 +97,17 @@ public class AppConfig {
         }
     }
 
+    @Nullable
+    public static File getExternalCopyTempDir() {
+        File dir = sContext.getExternalCacheDir();
+        File file;
+        if (null != dir && FileUtils.ensureDirectory(file = new File(dir, "copy"))) {
+            return file;
+        } else {
+            return null;
+        }
+    }
+
     @Nullable
     public static File getExternalParseErrorDir() {
         return getDirInExternalAppDir(PARSE_ERROR);