QAnyStringView: fix MSVC warning C4702

The previous fix attempt at 8ba8d1346a562347c398bdd0529d34f94f2ac698
does not work when C++20 mode is enabled.

MSVC optimizes away the "else" block but triggers warning C4702 on
"return true". Moving the return line into the "else" block ensures that
it is optimized away too.

Change-Id: I9ef02cd3631ff78091530b6fb2b91c2eddcbab5d
Pick-to: 6.5 6.4
Fixes: QTBUG-104836
Reviewed-by: Marc Mutz <marc.mutz@qt.io>
Reviewed-by: Yuhang Zhao <yuhangzhao@deepin.org>

src/corelib/text/qanystringview.h

@@ -122,8 +122,8 @@ private:
                 if (uchar(str[i]) > 0x7f)
                     return false;
             }
+            return true;
         }
-        return true;
 #endif
     }