Ensure we abort properly if open fails

Potentially this should be done for all read, open, and
write calls. But for the initial open there are also user
errors that must cause an abort.

src/fitting/ensemble-samplers/emcee.sl

@@ -1958,7 +1958,7 @@ private define file_exists (filename) %{{{
 private define emceeSetup (ship, steps, options) %{{{
 {
   variable leader, size, engine;
-  variable j, set;
+  variable j, set, err;
   
   engine = ship.engine;
   if (0 == engine.id) {
@@ -1995,7 +1995,15 @@ private define emceeSetup (ship, steps, options) %{{{
 
 	throw ReadError, sprintf("File '%s' does not exist", options.output.filename);
       }
-      options.output.open(engine);
+      try (err) {
+	options.output.open(engine);
+      }
+      catch AnyError:
+      {
+	if (ship.abort != NULL)
+	  ship.abort();
+	throw err.error, err.message; % forward error, make sure we aborted
+      }
     }
     else
     {
@@ -2009,7 +2017,15 @@ private define emceeSetup (ship, steps, options) %{{{
 
 	throw WriteError, sprintf("File '%s' exists.", options.output.filename);
       }
-      options.output.create(engine);
+      try (err) {
+	options.output.create(engine);
+      }
+      catch AnyError:
+      {
+	if (ship.abort != NULL)
+	  ship.abort();
+	throw err.error, err.message; % forward error
+      }
     }
 
     leader = engine.leader;