[minor] update the image field value if file's is_private value changed

frappe/core/doctype/file/file.py

@@ -76,6 +76,7 @@ class File(NestedSet):
 
 		if frappe.db.exists('File', {'name': self.name, 'is_folder': 0}):
 			if not self.is_folder and (self.is_private != self.db_get('is_private')):
+				old_file_url = self.file_url
 				private_files = frappe.get_site_path('private', 'files')
 				public_files = frappe.get_site_path('public', 'files')
 
@@ -91,6 +92,11 @@ class File(NestedSet):
 
 					self.file_url = "/private/files/{0}".format(self.file_name)
 
+			# update documents image url with new file url
+			if self.attached_to_doctype and self.attached_to_name and \
+				frappe.db.get_value(self.attached_to_doctype, self.attached_to_name, "image") == old_file_url:
+				frappe.db.set_value(self.attached_to_doctype, self.attached_to_name, "image", self.file_url)
+
 	def set_folder_size(self):
 		"""Set folder size if folder"""
 		if self.is_folder and not self.is_new():