fix base64 (==)

src/cpp/kazMisc.cpp

@@ -311,8 +311,7 @@ kaz::base64Decode (string &content) {
       buff [j] = 0;
     *q = buff [0] << 2 | (buff [1] & 0x30) >> 4;
     ++q;
-    --idx;
-    if (idx) {
+    if (idx > 2) {
       *q = buff [1] << 4 | (buff [2] & 0x3c) >> 2;
       ++q;
     }