dotnet_home: more robust

Author: scivision

+stdlib/dotnet_api.m

@@ -5,6 +5,7 @@
 try
   v = System.Environment.Version.Major;
 catch
+  % not empty because that breaks less-than logic
   v = -1;
 end
 

+stdlib/dotnet_home.m

@@ -1,9 +1,17 @@
 %% DOTNET_HOME give .NET RuntimeLocation
 
 function h = dotnet_home()
-try
-  h = dotnetenv().RuntimeLocation;
-catch
-  h = "";
+
+h = string.empty;
+
+try %#ok<TRYNC>
+
+  if NET.isNETSupported
+    % need to call this at least once or dotnetenv() is empty
+
+    h = dotnetenv().RuntimeLocation;
+  end
+
 end
+
 end