Fix crash if using a custom pandoc installation

Fixes #563

manuskript/exporter/basic.py

@@ -59,7 +59,7 @@ class basicExporter:
             run = self.customPath
         else:
             print("Error: no command for", self.name)
-            return
+            return None
         r = subprocess.check_output([run] + args)  # timeout=.2
         return r.decode("utf-8")
 

manuskript/exporter/pandoc/__init__.py

@@ -48,7 +48,14 @@ class pandocExporter(basicExporter):
             return ""
 
     def convert(self, src, args, outputfile=None):
-        args = [self.cmd] + args
+        if self.isValid() == 2:
+            run = self.cmd
+        elif self.isValid() == 1:
+            run = self.customPath
+        else:
+            print("Error: no command for pandoc")
+            return None
+        args = [run] + args
 
         if outputfile:
             args.append("--output={}".format(outputfile))

manuskript/importer/pandocImporters.py

@@ -38,6 +38,9 @@ class pandocImporter(abstractImporter):
 
         r = pandocExporter().run(args)
 
+        if r is None:
+            return None
+
         if formatTo == "opml":
             return self.opmlImporter.startImport("", parentItem,
                                             settingsWidget, fromString=r)