(Windows) Don't die if documentation not present

bin/FIJI.pm

@@ -32,7 +32,10 @@ use File::Spec;
 use Log::Log4perl qw(:easy);
 
 use constant FIJI_DIR => realpath(File::Spec->rel2abs("..", $FindBin::Bin));
-use constant FIJI_DOCUMENTATION_PATH => realpath(
+
+my $documentation_path;
+BEGIN {
+    my $pdf = 
         File::Spec->rel2abs(
             File::Spec->catfile(
                 "..",
@@ -41,8 +44,14 @@ use constant FIJI_DOCUMENTATION_PATH => realpath(
                 "fiji_user_guide.pdf"
             ),
             $FindBin::Bin
-    )
-);
+        );
+    
+    eval { $pdf = realpath($pdf) };
+    if ($@) {
+        $pdf = undef;
+    }
+};
+use constant FIJI_DOCUMENTATION_PATH => $documentation_path;
 
 use constant FIJI_MEDIA_PATH => realpath(
     File::Spec->rel2abs(

bin/Tk/FIJIUtils.pm

@@ -178,7 +178,14 @@ sub cross_platform_open {
 
 sub show_documentation {
     my $parent = shift;
+    if (!defined FIJI_DOCUMENTATION_PATH) {
+        my $d = $parent->FIJIModalDialog(-image     => error_image($parent),
+                                         -text      => "FIJI Documentation missing",
+                                         -title     => "Could not open documentation",);
+        $d->Show();
+    } else {
         return cross_platform_open($parent, FIJI_DOCUMENTATION_PATH);
+    }
 }
 
 sub show_about {