Replace post-increment with pre-increment

And post-decrement with pre-decrement.

src/base/net/smtp.cpp

@@ -67,7 +67,7 @@ namespace
         // ascii characters 0x36 ("6") and 0x5c ("\") are selected because they have large
         // Hamming distance (http://en.wikipedia.org/wiki/Hamming_distance)
 
-        for (int i = 0; i < key.length(); i++) {
+        for (int i = 0; i < key.length(); ++i) {
             innerPadding[i] = innerPadding[i] ^ key.at(i); // XOR operation between every byte in key and innerpadding, of key length
             outerPadding[i] = outerPadding[i] ^ key.at(i); // XOR operation between every byte in key and outerpadding, of key length
         }