Bug Fix: #4357 JS Form is sumitted on "enter" even if focus is inside a select field.

Bug Fix: #4357 JS Form is sumitted on "enter" even if focus is inside a select field.
https://sourceforge.net/p/phpmyadmin/bugs/4357/

This commit fixes the above problem on following Ajax dialog boxes:
- Index Add/Edit Dialog
- Routine Add/Edit Dialog
- Trigger Add/Edit Dialog
- Event Add/Edit Dialog

Signed-off-by: Ashutosh Dhundhara <ashutoshdhundhara@yahoo.com>