binext: fix crash on non-existent exiftool

Signed-off-by: Varun Patil <radialapps@gmail.com>

lib/Service/BinExt.php

@@ -131,11 +131,10 @@ class BinExt
             // get target file path
             $path = realpath(__DIR__."/../../exiftool-bin/exiftool-{$arch}-{$libc}");
 
-            // Set config
+            // make sure it exists
+            if ($path && file_exists($path)) {
                 Util::setSystemConfig('memories.exiftool', $path);
 
-            // make sure it exists
-            if (file_exists($path)) {
                 return $path;
             }
         }