winGRASS-R-integration: fix check R installation

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@67473 15284696-431f-4ddb-bdfa-cd5b030d7da7

mswindows/env.bat

@@ -19,4 +19,4 @@ IF EXIST "%ProgramFiles%\RStudio\bin\rstudio.exe" set PATH=%PATH%;%ProgramFiles%
 
 REM set R temporarily to %PATH%
 
-IF EXIST "%GISBASE%\extrabin\R.exe" %GISBASE%\extrabin\R path
+IF EXIST "%ProgramFiles%\R\" %GISBASE%\extrabin\R path