fix unexpected global varible in loop

[xiangnan]

Hi! 👋

Firstly, thanks for your work on this project! 🙂

Today I used patch-package to patch exif-js@2.3.0 for the project I'm working on.

Here is the diff that solved my problem:

diff --git a/node_modules/exif-js/exif.js b/node_modules/exif-js/exif.js
index 35395cf..1984373 100644
--- a/node_modules/exif-js/exif.js
+++ b/node_modules/exif-js/exif.js
@@ -738,7 +738,7 @@
 
     function getStringFromDB(buffer, start, length) {
         var outstr = "";
-        for (n = start; n < start+length; n++) {
+        for (var n = start; n < start+length; n++) {
             outstr += String.fromCharCode(buffer.getUint8(n));
         }
         return outstr;

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