Cleanup in _simple_upsert_txn

Bail out early to reduce indentation

synapse/storage/_base.py

@@ -493,7 +493,7 @@ class SQLBaseStore(object):
         if lock:
             self.database_engine.lock_table(txn, table)
 
-        # Try to update
+        # First try to update.
         sql = "UPDATE %s SET %s WHERE %s" % (
             table,
             ", ".join("%s = ?" % (k,) for k in values),
@@ -502,8 +502,11 @@ class SQLBaseStore(object):
         sqlargs = values.values() + keyvalues.values()
 
         txn.execute(sql, sqlargs)
-        if txn.rowcount == 0:
-            # We didn't update and rows so insert a new one
+        if txn.rowcount > 0:
+            # successfully updated at least one row.
+            return False
+
+        # We didn't update any rows so insert a new one
         allvalues = {}
         allvalues.update(keyvalues)
         allvalues.update(values)
@@ -515,10 +518,8 @@ class SQLBaseStore(object):
             ", ".join("?" for _ in allvalues)
         )
         txn.execute(sql, allvalues.values())
-
+        # successfully inserted
         return True
-        else:
-            return False
 
     def _simple_select_one(self, table, keyvalues, retcols,
                            allow_none=False, desc="_simple_select_one"):