etc/config.csh/paraview: avoid ParaView_DIR: Undefined variable.

Patch contributed by Bruno Santos
Resolves bug-report http://bugs.openfoam.org/view.php?id=2309

etc/config.csh/paraview

@@ -34,6 +34,8 @@
 #
 #------------------------------------------------------------------------------
 
+if ( ! $?ParaView_DIR ) setenv ParaView_DIR
+
 # Clean the PATH
 set cleaned=`$WM_PROJECT_DIR/bin/foamCleanPath "$PATH" "$ParaView_DIR $WM_THIRD_PARTY_DIR/platforms/$WM_ARCH$WM_COMPILER/cmake- $WM_THIRD_PARTY_DIR/platforms/$WM_ARCH$WM_COMPILER/paraview-"`
 if ( $status == 0 ) setenv PATH $cleaned