autfilt: diagnose non-existant files

* src/bin/autfilt.cc: Catch exception.
* src/tgbatest/hoaparse.test: Test it.

src/bin/autfilt.cc

@@ -391,7 +391,14 @@ main(int argc, char** argv)
   post.set_level(level);
 
   hoa_processor processor(post);
-  if (processor.run())
-    return 2;
+  try
+    {
+      if (processor.run())
+	return 2;
+    }
+  catch (const std::runtime_error& e)
+    {
+      error(2, 0, "%s", e.what());
+    }
   return 0;
 }

src/tgbatest/hoaparse.test

@@ -717,3 +717,7 @@ input:4.7-242: unclosed string
 input:4.7-242: syntax error, unexpected end of file, expecting string
 autfilt: failed to read automaton from input
 EOF
+
+expecterr non-existant<<EOF
+autfilt: Cannot open file non-existant
+EOF