Accept relative paths in the IdeHandler API's "filename" key

tfw/components/ide/ide_handler.py

@@ -76,7 +76,9 @@ class IdeHandler:
         if 'patterns' in message:
             self.filemanager.patterns = message['patterns']
         try:
-            message['filename'] = message.get('filename') or self.initial_file
+            message['filename'] = self.filemanager.find_file(
+                message.get('filename') or self.initial_file
+            )
             message['content'] = self.filemanager.read_file(message['filename'])
         except (PermissionError, ValueError):
             message['content'] = 'You have no permission to open that file :('