Make OpenBytes call OpenMapOrArray even if the buffer is NULL. (#156)

It's not clear to me was the call was wrapped in this condition, but
since OpenMapOrArray is responsible for recording nesting information,
this broke any OpenBytes/CloseBytes that were designed to work with both
NULL and non-NULL buffers.
diff --git a/src/qcbor_encode.c b/src/qcbor_encode.c
index 3a0a968..26d86ce 100644
--- a/src/qcbor_encode.c
+++ b/src/qcbor_encode.c
@@ -986,18 +986,16 @@
 void QCBOREncode_OpenBytes(QCBOREncodeContext *pMe, UsefulBuf *pPlace)
 {
    *pPlace = UsefulOutBuf_GetOutPlace(&(pMe->OutBuf));
-   if(!UsefulBuf_IsNULL(*pPlace)) {
 #ifndef QCBOR_DISABLE_ENCODE_USAGE_GUARDS
-      // TODO: is this right?
-      uint8_t uMajorType = Nesting_GetMajorType(&(pMe->nesting));
-      if(uMajorType == CBOR_MAJOR_NONE_TYPE_OPEN_BSTR) {
-         pMe->uError = QCBOR_ERR_OPEN_BYTE_STRING;
-         return;
-      }
+   // TODO: is this right?
+   uint8_t uMajorType = Nesting_GetMajorType(&(pMe->nesting));
+   if(uMajorType == CBOR_MAJOR_NONE_TYPE_OPEN_BSTR) {
+      pMe->uError = QCBOR_ERR_OPEN_BYTE_STRING;
+      return;
+   }
 #endif /* QCBOR_DISABLE_ENCODE_USAGE_GUARDS */
 
-      QCBOREncode_OpenMapOrArray(pMe, CBOR_MAJOR_NONE_TYPE_OPEN_BSTR);
-   }
+   QCBOREncode_OpenMapOrArray(pMe, CBOR_MAJOR_NONE_TYPE_OPEN_BSTR);
 }