Do not include headers in cv namespace

That creates some conflict on some windows platform with blaze.

modules/imgproc/src/drawing_text.cpp

@@ -42,9 +42,6 @@
 #include <unordered_map>
 #include "zlib.h"
 
-namespace cv
-{
-
 #ifdef HAVE_HARFBUZZ
 
 #include <hb.h>
@@ -59,6 +56,9 @@ namespace cv
 
 //////////////////////////////////////////////////////////////////////////////////////
 
+namespace cv
+{
+
 typedef struct BuiltinFontData
 {
     const uchar* gzdata;