build: fix detection of Visual Studio 2019

If Visual Studio 2017 is not found, attempt to find Visual Studio 2019.

Author: richardlau

vcbuild.bat

@@ -244,7 +244,7 @@ if %target_arch%==x86 if %msvs_host_arch%==x86 set vcvarsall_arg=x86
 if defined target_env if "%target_env%" NEQ "vs2017" goto vs-set-2019
 echo Looking for Visual Studio 2017
 call tools\msvs\vswhere_usability_wrapper.cmd "[15.0,16.0)"
-if "_%VCINSTALLDIR%_" == "__" goto msbuild-not-found
+if "_%VCINSTALLDIR%_" == "__" goto vs-set-2019
 if defined msi (
   echo Looking for WiX installation for Visual Studio 2017...
   if not exist "%WIX%\SDK\VS2017" (