Return the text content from file if it exists.

getTextContent is now more consistent with the other accessor (getContentType, getTitle, ...).

product/ERP5/Document/EmailDocument.py

@@ -442,7 +442,7 @@ class EmailDocument(TextDocument):
     to display the content of an email.
     """
     self._checkConversionFormatPermission(None)
-    if not self.hasFile() or self._baseGetTextContent() is not None:
+    if not self.hasFile():
       # Return the standard text content if no file was provided
       # Or standard text content is not empty.
       if default is _MARKER: