Fix #12193 - problem with update of SQL query in DB manager

In the scenario described in the bug report, the selected text was empty,
but editor's hasSelectedText() would still return True

Author: wonder-sk

python/plugins/db_manager/dlg_sql_window.py

@@ -140,10 +140,8 @@ def clearSql(self):
 
   def executeSql(self):
 
-    sql = ""
-    if self.editSql.hasSelectedText():
-        sql = self.editSql.selectedText()
-    else:
+    sql = self.editSql.selectedText()
+    if len(sql) == 0:
         sql = self.editSql.text()
 
     if sql == "":