osgeo4w: fix postinstall scripts (fixes #17993)

ms-windows/osgeo4w/postinstall-desktop.bat

@@ -6,7 +6,7 @@ REM get short path without blanks
 for %%i in ("%OSGEO4W_ROOT%") do set O4W_ROOT=%%~fsi
 if "%OSGEO4W_DESKTOP%"=="" set OSGEO4W_DESKTOP=~$folder.common_desktop$
 
-"%OSGEO4W_ROOT%\bin\@package@.bat" --exit
+call "%OSGEO4W_ROOT%\bin\@package@.bat" --postinstall
 
 if not %OSGEO4W_MENU_LINKS%==0 mkdir "%OSGEO4W_STARTMENU%"
 if not %OSGEO4W_DESKTOP_LINKS%==0 mkdir "%OSGEO4W_DESKTOP%"

ms-windows/osgeo4w/postinstall-dev.bat

@@ -10,7 +10,7 @@ for %%g in (@grassversions@) do (
 	copy "%OSGEO4W_ROOT%\bin\@package@-bin.exe" "%OSGEO4W_ROOT%\bin\@package@-bin-g%%g.exe"
 	copy "%OSGEO4W_ROOT%\bin\@package@-bin.vars" "%OSGEO4W_ROOT%\bin\@package@-bin-g%%g.vars"
 	textreplace -std -t bin\@package@-g%%g.bat
-	"%OSGEO4W_ROOT%\bin\@package@-g%%g.bat" --exit
+	call "%OSGEO4W_ROOT%\bin\@package@-g%%g.bat" --postinstall
 
 	if not %OSGEO4W_MENU_LINKS%==0 nircmd shortcut "%OSGEO4W_ROOT%\bin\@package@-bin-g%%g.exe" "%OSGEO4W_STARTMENU%" "QGIS Desktop @version@ with GRASS %%g (Nightly)"
 	if not %OSGEO4W_DESKTOP_LINKS%==0 nircmd shortcut "%OSGEO4W_ROOT%\bin\@package@-bin-g%%g.exe" "%OSGEO4W_DESKTOP%" "QGIS Desktop @version@ with GRASS %%g (Nightly)"

ms-windows/osgeo4w/postinstall-grass.bat

@@ -4,7 +4,7 @@ if "%OSGEO4W_DESKTOP%"=="" set OSGEO4W_DESKTOP=~$folder.common_desktop$
 
 copy bin\@package@-bin.exe bin\@package@-bin-grass@grassmajor@.exe
 copy bin\@package@-bin.vars bin\@package@-bin-grass@grassmajor@.vars
-"%OSGEO4W_ROOT%\bin\@package@-grass@grassmajor@.bat" --exit
+call "%OSGEO4W_ROOT%\bin\@package@-grass@grassmajor@.bat" --postinstall
 
 if not %OSGEO4W_MENU_LINKS%==0 mkdir "%OSGEO4W_STARTMENU%"
 if not %OSGEO4W_DESKTOP_LINKS%==0 mkdir "%OSGEO4W_DESKTOP%"

src/app/mainwin.cpp

@@ -42,7 +42,7 @@ int CALLBACK WinMain( HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdL
 {
   std::string basename( moduleExeBaseName() );
 
-  if ( getenv( "OSGEO4W_ROOT" ) )
+  if ( getenv( "OSGEO4W_ROOT" ) && __argc == 2 && strcmp( __argv[1], "--postinstall" ) == 0 )
   {
     std::string envfile( basename + ".env" );
 
@@ -90,41 +90,36 @@ int CALLBACK WinMain( HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdL
       }
     }
 
-    if ( __argc == 2 && strcmp( __argv[1], "--exit" ) == 0 )
-    {
-      return EXIT_SUCCESS;
-    }
+    return EXIT_SUCCESS;
   }
-  else
+
+  try
   {
-    try
-    {
-      std::ifstream file;
-      file.open( basename + ".env" );
+    std::ifstream file;
+    file.open( basename + ".env" );
 
-      std::string var;
-      while ( std::getline( file, var ) )
+    std::string var;
+    while ( std::getline( file, var ) )
+    {
+      if ( _putenv( var.c_str() ) < 0 )
       {
-        if ( _putenv( var.c_str() ) < 0 )
-        {
-          std::string message = "Could not set environment variable:" + var;
-          showError( message, "Error loading QGIS" );
-          return EXIT_FAILURE;
-        }
+        std::string message = "Could not set environment variable:" + var;
+        showError( message, "Error loading QGIS" );
+        return EXIT_FAILURE;
       }
     }
-    catch ( std::ifstream::failure e )
-    {
-      std::string message = "Could not read environment file " + basename + ".env" + " [" + e.what() + "]";
-      showError( message, "Error loading QGIS" );
-      return EXIT_FAILURE;
-    }
+  }
+  catch ( std::ifstream::failure e )
+  {
+    std::string message = "Could not read environment file " + basename + ".env" + " [" + e.what() + "]";
+    showError( message, "Error loading QGIS" );
+    return EXIT_FAILURE;
   }
 
 #ifdef _MSC_VER
   HINSTANCE hGetProcIDDLL = LoadLibrary( "qgis_app.dll" );
 #else
-  // MinGW
+// MinGW
   HINSTANCE hGetProcIDDLL = LoadLibrary( "libqgis_app.dll" );
 #endif