Update php_base64_decode() to cover Bug52327

Strict mode should fail on padding characters mid-stream.

hphp/runtime/base/zend/zend_string.cpp

@@ -1884,7 +1884,15 @@ static unsigned char *php_base64_decode(const unsigned char *str,
   /* run through the whole string, converting as we go */
   while ((ch = *current++) != '\0' && length-- > 0) {
     if (ch == base64_pad) {
-      if (*current != '=' && (i % 4) == 1) {
+      if (*current != '=' && ((i % 4) == 1 || (strict && length > 0))) {
+        if ((i % 4) != 1) {
+          while (isspace(*(++current))) {
+            continue;
+          }
+          if (*current == '\0') {
+            continue;
+          }
+        }
         free(result);
         return nullptr;
       }