[minor] show the child table fields lable in Auto Email Report

frappe/core/doctype/report/report.py

@@ -147,10 +147,13 @@ class Report(Document):
 				limit=limit,
 				user=user)
 
-			meta = frappe.get_meta(self.ref_doctype)
-
-			columns = [meta.get_field(c[0]) or frappe._dict(label=meta.get_label(c[0]), fieldname=c[0])
-				for c in columns]
+			_columns = []
+			for column in columns:
+				meta = frappe.get_meta(column[1])
+				field = [meta.get_field(column[0]) 
+					or frappe._dict(label=meta.get_label(column[0]), fieldname=column[0])]
+				_columns.extend(field)
+			columns = _columns
 
 			out = out + [list(d) for d in result]